Sodium ion batteries

ABSTRACT

Sodium ion batteries are based on sodium based active materials selected among compounds of the general formula:  
     A a M b (XY 4 ) c Z d ,  
     wherein A comprises sodium, M comprises one or more metals, comprising at least one metal which is capable of undergoing oxidation to a higher valence state, Z is OH or halogen, and XY 4  represents phosphate or a similar group. The anode of the battery includes a carbon material that is capable of inserting sodium ions. The carbon anode cycles reversibly at a specific capacity greater than 100 mAh/g.

FIELD OF THE INVENTION

[0001] The invention relates to sodium ion batteries. More specifically,the invention relates to anode and cathode materials that reversiblecycle sodium ions.

BACKGROUND OF THE INVENTION

[0002] Non-aqueous lithium electrochemical cells typically include ananode, an electrolyte comprising a lithium salt that is dissolved in oneor more organic solvents and a cathode of an electrochemically activematerial, typically a chalcogenide of a transition metal.

[0003] Such cells, in an initial condition, are not charged. In order tobe used to deliver electrochemical energy, such cells must be charged inorder to transfer lithium to the anode from the lithium-containingcathode. During the initial charge, lithium ions are extracted from thecathode and transferred to the anode. During discharge, lithium ionsfrom the anode pass through the liquid electrolyte to theelectrochemically active cathode material of the cathode where the ionsare taken up with the simultaneous release of electrical energy. Duringcharging, the flow of ions is reversed so that lithium ions pass fromthe electrochemically active material through the electrolyte and areplated back onto the anode. Upon subsequent charge and discharge, thelithium ions (Li⁺) are transported between the electrodes. Suchrechargeable batteries, having no free metallic species are calledrechargeable ion batteries or rocking chair batteries. Rechargeablebatteries and non-aqueous lithium electrochemical cells are discussed inU.S. Pat. Nos. 6,203,946; 5,871,866; 5,540,741; 5,460,904; 5,441,830;5,418,090; 5,130,211; 4,464,447; and 4,194,062 the disclosures of whichare incorporated herein by reference.

[0004] Sodium based active materials are described herein for use in ionbatteries. The active materials may potentially offer some advantages,such as lower materials costs and the ability to utilize superiorelectrolyte systems. Until recently the problem with the practicalrealization of sodium ion batteries has been the lack of both anode(negative) and cathode (positive) electrode materials that couldreversibly cycle sodium ions.

SUMMARY OF THE INVENTION

[0005] Operation of a sodium-ion battery is demonstrated herein to beanalogous to the previously described lithium ion battery operation. Thesodium ions are initially extracted from the cathode containing thesodium based active material and transferred to the anode. As previouslydiscussed in relation to the lithium ion battery, during dischargesodium ions from the anode pass through the liquid electrolyte to theelectrochemically active sodium based material of the cathode where theions are taken up with the simultaneous release of electrical energy.Therefore, the electrochemical performance of the sodium ionelectrochemical cell is analogous to the previously established lithiumion cell performance.

[0006] The invention provides sodium transition metal compounds suitablefor incorporation as the (positive) cathode active materials in sodiumion applications. These materials have relatively high operatingpotential and good specific capacity. The invention further provides anintercalation anode that can insert and de-insert (release) sodium ionsduring a charge-discharge cycle.

[0007] In another embodiment, a battery comprises a cathode, an anode,and an electrolyte. In one embodiment the cathode contains anelectrochemically active sodium based material. The sodium based activematerial is primarily a sodium metal phosphate selected from compoundsof the general formula:

A_(a)M_(b)(XY₄)_(c)Z_(d),

[0008] wherein

[0009] (a) A is selected from the group consisting of sodium andmixtures of sodium with other alkali metals, and 0<a≦9;

[0010] (b) M comprises one or more metals, comprising at least one metalwhich is capable of undergoing oxidation to a higher valence state, and1≦b≦3;

[0011] (c) XY₄ is selected from the group consisting of X′O_(4−x)Y′_(x),X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is P, As, Sb, Si,Ge, S, and mixtures thereof; X″ is P, As, Sb, Si, Ge and mixturesthereof; Y′ S is halogen; 0≦x<3; and 0<y<4; and 0<c≦3;

[0012] (d) Z is OH, halogen, or mixtures thereof, and 0≦d≦6; and

[0013] wherein M, X, Y, Z, a, b, c, d, x and y are selected so as tomaintain electroneutrality of the compound.

[0014] Non-limiting examples of preferred sodium containing activematerials include NaVPO₄F, Na_(1+y)VPO₄F_(1+y), NaVOPO₄, Na₃V₂(PO₄)₂F₃,Na₃V₂(PO₄)₃, NaFePO₄, NaFe_(x)Mg_(1−x)PO₄, Na₂FePO₄F and combinationsthereof, wherein 0<x<1, and −0.2≦y≦0.5. Another preferred activematerial has the general formula Li_(1−z)Na_(z)VPO₄F wherein 0<z<1. Inaddition to vanadium (V), various transition metals and non-transitionmetal elements can be used individually or in combination to preparesodium based active materials.

[0015] In an alternate embodiment the anode of the battery includes ahard carbon that is capable of inserting sodium ions. The hard carbonanode cycles reversibly at a specific capacity greater than 100 mAh/g.In a further alternate embodiment the anode including a hard carboncapable of inserting sodium and/or lithium ions reversibly cycles at aspecific capacity greater than 200 mAh/g.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is an x-ray diffraction pattern for NaVPO₄F prepared byreaction of NaF with VPO₄.

[0017]FIG. 2 is an x-ray diffraction pattern of NaVPO₄F formed in alimited air atmosphere.

[0018]FIG. 3 is an x-ray diffraction pattern for a materialNa_(x)VPO₄F_(x), synthesized in a limited air atmosphere.

[0019]FIG. 4 is an extended range x-ray diffraction pattern (2Π=10-80°for NaVPO₄F prepared with a 20% mass excess NaF.

[0020]FIG. 5 is an x-ray diffraction pattern for NaVPO4F prepared byreaction of NH4F, Na2CO3, and VPO4.

[0021]FIG. 6 is an x-ray diffraction pattern for Li₀ ₀₅Na_(0.95)VPO₄F.

[0022]FIG. 7 is an x-ray diffraction pattern for Li₀ ₉₅Na₀ ₀₅VPO₄F.

[0023]FIG. 8 is an x-ray diffraction pattern of Na₃V₂ (PO₄)₂F₃.

[0024]FIG. 9 is an x-ray diffraction pattern of Na₃V₂ (PO₄)₂F3 preparedfrom VPO₄/NAF in air.

[0025]FIG. 10 is an x-ray diffraction pattern for a commercial hardcarbon.

[0026]FIG. 11 shows variation in cell voltage versus cathode specificcapacity for a sodium ion cell at a cathode to anode mass ratio of2.67:1.

[0027]FIG. 12 shows variation in cell voltage versus cathode specificcapacity for a sodium ion cell at a cathode to anode mass ratio of2.46:1.

[0028]FIG. 13 shows EVS differential capacity data for a sodium ioncell.

[0029]FIG. 14 shows a particle distribution of hard carbon.

[0030]FIG. 15 shows a scanning electron micrograph of hard carbon.

DETAILED DESCRIPTION OF THE INVENTION

[0031] In one embodiment, the invention provides new active materialsuseful as cathodes in sodium ion batteries. The active materials, whenformulated into a cathode composition are capable of reversibly cyclingsodium ions between the cathode and the anode. In a preferredembodiment, the electrochemical active materials of the inventioninclude sodium transition metal phosphates and sodium transition metalfluorophosphates. Such active materials can take on a range ofstoichiometries as are illustrated in non-limiting examples below. Amongthe sodium transition metal phosphates and fluorophosphates, thetransition metals includewithout limitation those of groups 4 through11, inclusive, of the periodic table. Preferred transition metalsinclude those of the first transition period, namely Ti, V, Cr, Mn, Fe,Co, and Ni. The active materials may also include a mixture oftransition metals, or mixtures of transition metals and non-transitionmetals. A preferred transition metal is vanadium. Vanadium species thathave been synthesized and demonstrated to be effective aselectrochemically active cathode materials for use in sodium ionbatteries include, without limitation, NaVPO₄F, Na_(1+y)VPO₄F_(1+y),NaVOPO₄, Na₃V₂(PO₄)₂F₃, NaFe_(x)Mg_(1−x)PO₄, and Na₃V₂(PO₄)₃. In theformulas, 0<x<1 and the value of y ranges from −0.2 to about 0.5. Anelectrochemically active transition metal material having the formulaLi_(1−z)Na_(z)VPO₄F wherein 0<z<1 can be further applied.

[0032] In another embodiment, the active materials have a generalformula

A_(a)M_(b)(XY₄)_(c)Z_(d),

[0033] wherein

[0034] A is selected from the group consisting of sodium and mixtures ofsodium and other alkali metals, and 0<a≦9;

[0035] M comprises one or more metals, comprising at least one metalcapable of undergoing oxidation to a higher valence state, and 1≦b≦3;

[0036] XY₄ is selected from the group consisting of X′O_(4−x)Y′_(x),X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is P, As, Sb, Si,Ge, V, S, or mixtures thereof; X″ is P, As, Sb, Si, V, Ge, or mixturesthereof; Y′ is S, N, or halogen; 0≦x≦3; and 0<y≦2; and 0<c≦3;

[0037] Z is OH, halogen, or mixtures thereof, and 0≦d≦6; and

[0038] and wherein M, XY₄, Z, a, b, c, d, x and y are selected so as tomaintain electroneutrality of said compound.

[0039] In one preferred embodiment, c=3 in the formula above. In otherembodiments, when d=0 and XY₄ is phosphate, the active materials of theabove formula correspond to the transition metal phosphates describedabove. When d is greater than 0, the materials of the formula correspondto the transition metal fluorophosphates. In other aspects, the activematerials of the above formula represent transition metal phosphateswhere the phosphate group is partially or completely replaced by groupssuch as silicate, sulfate, germanate, antimonate, arsenate,monofluoromonophosphate, difluoromonophosphate, and the like, as well assulfur analogs of the above.

[0040] A is selected from the group consisting of Na (sodium), andmixtures of sodium and other alkali metals. A preferred other alkalimetal is lithium. In a preferred embodiment, A is a mixture of Li withNa, a mixture of Na with K, or a mixture of Li, Na and K. Preferably “a”is from about 0.1 to about 6, more preferably from about 0.2 to about 6.Where c=1, a is preferably from about 0.1 to about 3, preferably fromabout 0.2 to about 2. In a preferred embodiment, where c=1, a is lessthan about 1. In another preferred embodiment, where c=1, a is about 2.Preferably “a” is from about 0.8 to about 1.2. Where c=2, a ispreferably from about 0.1 to about 6, preferably from about 1 to about6. Where c=3, a is preferably from about 0.1 to about 6, preferably fromabout 2 to about 6, preferably from about 3 to about 6. In anotherembodiment, “a” is preferably from about 0.2 to about 1.0.

[0041] In a preferred embodiment, removal of alkali metal from theelectrode active material is accompanied by a change in oxidation stateof at least one of the metals comprising M. The amount of said metalthat is available for oxidation in the electrode active materialdetermines the amount of alkali metal that may be removed. Such conceptsare, in general application, well known in the art, e.g., as disclosedin U.S. Pat. No. 4,477,541, Fraioli, issued Oct. 16, 1984; and U.S. Pat.No. 6,136,472, Barker, et al., issued Oct. 24, 2000, both of which areincorporated by reference herein.

[0042] Referring to the general formula A_(a)M_(b)(XY₄)_(c)Z_(d), theamount (a′) of alkali metal that can be removed, as a function of thequantity of M (b′) and valence (V^(M)) of oxidizable metal, is

a′=b′(ΔV ^(M)),

[0043] where ΔV^(M) is the difference between the valence state of themetal in the active material and a valence state readily available forthe metal. (The term oxidation state and valence state are used in theart interchangeably.) For example, for an active material comprisingiron (Fe) in the +2 oxidation state, ΔV^(M)=1, wherein iron may beoxidized to the +3 oxidation state (although iron may also be oxidizedto a +4 oxidation state in some circumstances). If b=1 (one atomic unitof Fe per atomic unit of material), the maximum amount (a′) of alkalimetal (oxidation state +1) that can be removed during cycling of thebattery is 1 (one atomic units of alkali metal). If b=1.25, the maximumamount of (a′) of alkali metal that can be removed during cycling of thebattery is 1.25.

[0044] The value of “b” and the total valence of M in the activematerial must be such that the resulting active material is electricallyneutral (i.e., the positive charges of all anionic species in thematerial balance the negative charges of all cationic species).

[0045] M comprises at least one element capable of undergoing oxidationto a higher oxidation state. Such elements M may be, in general, atransition metal selected from the group consisting of elements fromGroups 4-11 of the Periodic Table. As referred to herein, “Group” refersto the Group numbers (i.e., columns) of the Periodic Table as defined inthe current IUPAC Periodic Table. See, e.g., U.S. Pat. No. 6,136,472,Barker et al., issued Oct. 24, 2000, incorporated by reference herein.In another preferred embodiment, M further comprises a non-transitionmetal selected from Groups 2, 3, 12, 13, or 14 of the Periodic Table.

[0046] In another preferred embodiment, preferably where c=1, Mcomprises CO_(e),Fe_(f)M¹ _(g)M² _(h)M³ _(i), wherein M¹ is at least onetransition metal from Groups 4 to 11, M² is at least one +2 oxidationstate non-transition metal, M³ is a +3 oxidation state non transitionelement,e≧0,f≧0,g≧0,h≧0,i≧0 and (e+f+g+h+i)=b. Preferably, at least oneof e and f are greater than zero, more preferably both. In a preferredembodiment 0<(e+f+g+h+i)≦2, more preferably 0.8≦(e+f+g+h+i)≦1.2, andeven more preferably 0.9≦(e+f+g+h+_i)≦1.0. Preferably, e≧0.5, morepreferably e≧0.8. Preferably, 0.01≦f≦0.5, more preferably 0.05≦f≦0.15.Preferably, 0.01≦g≦0.5, more preferably 0.05≦g≦0.2. In a preferredembodiment, (h+i)>1, preferably 0.01≦(h+i)≦0.5, and even more preferably0.01≦(h+i)≦0.1. Preferably, 0.01≦h≦0.2, more preferably 0.01≦h≦0.1.Preferably 0.01≦i≦0.2, more preferably 0.01≦i≦0.1.

[0047] Transition metals useful herein, in addition to Fe and Co,include those selected from the group consisting of Ti (Titanium), V(Vanadium), Cr (Chromium), Mn (Manganese), Fe (Iron), Co (Cobalt), Ni(Nickel), Cu (Copper), Zr (Zirconium), Nb (Niobium), Mo (Molybdenum), Ru(Ruthenium), Rh (Rhodium), Pd (Palladium), Ag (Silver), Cd (Cadmium), Hf(Hafnium), Ta (Tantalum), W (Tungsten), Re (Rhenium), Os (Osmium), Ir(Iridium), Pt (Platinum), Au (Gold), Hg (Mercury), and mixtures thereof.Preferred are the first row transition series (the 4th Period of thePeriodic Table), selected from the group consisting of Ti, V, Cr, Mn,Fe, Co, Ni, Cu, and mixtures thereof. Particularly preferred transitionmetals include those selected from the group consisting of Fe, Co, Mn,and mixtures thereof. In a preferred embodiment, M is Co_(1−m)Fe_(m),where 0<m≦0.5. Preferably 0.01<m≦0.1. Although, a variety of oxidationstates for such transition metals is available, in some embodiments itis most preferable that the transition metals have a +2 oxidation state.

[0048] In a preferred embodiment, M further comprises non-transitionmetals or metalloids. In a preferred embodiment, the non-transitionmetals or metalloids are not readily capable of undergoing oxidation toa higher valence state in the electrode active material under normaloperating conditions. Among such elements are those selected from thegroup consisting of Group 2 elements, particularly Be (Beryllium), Mg(Magnesium), Ca (Calcium), Sr (Strontium), Ba (Barium); Group 3elements, particularly Sc (Scandium), Y (Yttrium), and the lanthanides,particularly La (Lanthanum), Ce (Cerium), Pr (Praseodymium), Nd(Neodymium), Sm (Samarium); Group 12 elements, particularly Zn (zinc)and Cd (cadmium); Group 13 elements, particularly B (Boron), Al(Aluminum), Ga (Gallium), In (Indium), Tl (Thallium); Group 14 elements,particularly Si (Silicon), Ge (Germanium), Sn (Tin), and Pb (Lead);Group 15 elements, particularly As (Arsenic), Sb (Antimony), and Bi(Bismuth); Group 16 elements, particularly Te (Tellurium); and mixturesthereof. Preferred non-transition metals include the Group 2 elements,Group 12 elements, Group 13 elements, and Group 14 elements.Particularly preferred non-transition elements include those selectedfrom the group consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, Al, andmixtures thereof. Particularly preferred are non-transition metalsselected from the group consisting of Mg, Ca, Zn, Ba, Al, and mixturesthereof.

[0049] As further discussed herein, “b” is selected so as to maintainelectroneutrality of the electrode active material. In a preferredembodiment, where c=1, b is from about 1 to about 2, preferably about 1.In another preferred embodiment, where c=2, b is from about 2 to about3, preferably about 2.

[0050] XY₄ is selected from the group consisting of X′O_(4−x)Y′_(x),X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is P(phosphorus), As (arsenic), Sb (antimony), Si (silicon), V (vanadium),Ge (germanium), S (sulfur), or mixtures thereof; X″ is P, As, Sb, Si, V,Ge or mixtures thereof. In a preferred embodiment, X′ and X″ are eachselected from the group consisting of P, Si, and mixtures thereof. In aparticularly preferred embodiment, X′ and X″ are P. Y is preferablyhalogen, more preferably F (fluorine).

[0051] In a preferred embodiment 0≦x≦3; and 0<y≦2, such that a portionof the oxygen (O) in the XY₄ moiety is substituted with halogen,nitrogen, or sulfur. In another preferred embodiment, x and y are 0. Ina particularly preferred embodiment XY₄ is X′O₄, where X′ is preferablyP or Si, more preferably P. In another particularly preferredembodiment, XY₄ is PO_(4−x)Y′_(x), where Y′ is halogen or nitrogen, and0<x≦1. Preferably 0.01≦x≦0.05, more preferably 0.02≦x≦0.03.

[0052] Z is OH, halogen, or mixtures thereof. In a preferred embodiment,Z is selected from the group consisting of OH (hydroxyl), F (fluorine),Cl (chlorine), Br (bromine) and mixtures thereof. In a preferredembodiment, Z is OH. In another preferred embodiment, Z is F, ormixtures of F with OH, Cl, or Br. In one preferred embodiment, d=0. Inanother preferred embodiment, d>0, preferably from about 0.1 to about 6,more preferably from about 0.2 to about 6. In such embodiments, wherec=1, d is preferably from about 0.1 to about 3, preferably from about0.2 to about 2. In a preferred embodiment, where c=1, d is about 1.Where c=2, d is preferably from about 0.1 to about 6, preferably fromabout 1 to about 6. Where c=3, d is preferably from about 0.1 to about6, preferably from about 2 to about 6, preferably from about 3 to about6. The composition of M, X, Y, Z and the values of a, b, c, d, x, and yare selected so as to maintain electroneutrality of the electrode activematerial. As referred to herein “electroneutrality” is the state of theelectrode active material wherein the sum of the positively chargedspecies (e.g., A and M) in the material is equal to the sum of thenegatively charged species (e.g. XY₄) in the material. Preferably, theXY₄ moieties are comprised to be, as a unit moiety, an anion having acharge of −2, −3, or −4, depending on the selection of X. When XY₄ is amixture of groups such as the preferred phosphates and phosphatesubstitutes discussed above, the net charge on the XY₄ anion may take onnon-integer values, depending on the charge and composition of theindividual groups XY₄ in the mixture.

[0053] (a) The values of a, b, c, d, x, and y may result instoichiometric or non-stoichiometric formulas for the electrode activematerials. In a preferred embodiment, the values of a, b, c, d, x, and yare all integer values, resulting in a stoichiometric formula. Inanother preferred embodiment, one or more of a, b, c, d, x and y mayhave non-integer values. It is understood, however, in embodimentshaving a lattice structure comprising multiple units of anon-stoichiometric formula A_(a)M_(b)(XY₄)_(c)Z_(d), that the formulamay be stoichiometric when looking at a multiple of the unit. That is,for a unit formula where one or more of a, b, c, d, x, or y is anon-integer, the values of each variable become an integer value withrespect to a number of units that is the least common multiplier of eachof a, b, c, d, x and y. For example, the active materialLi₂Fe_(0.5)Mg_(0.5)PO₄F is non-stoichiometric. However, in a materialcomprising two of such units in a lattice structure, the formula isLi₄FeMg(PO₄)₂F₂.

[0054] A preferred electrode active material embodiment comprises acompound of the formula

A_(a)M_(b)(PO₄)Z_(d),

[0055] wherein

[0056] (a) A is sodium or a mixture of sodium and other alkali metalsand 0.1<a≦4;

[0057] (b) M comprises at least one transition metal capable ofundergoing oxidation to a higher oxidation state and 1≦b≦3; and

[0058] (c) Z comprises halogen, and 0≦d≦4; and

[0059] wherein M, Z, a, b, and d are selected so as to maintainelectroneutrality of said compound.

[0060] In a preferred embodiment, M is M′_(1−m)M″_(m), where M′ is atleast one transition metal from Groups 4 to 11 of the Periodic Table; M″is at least one element which is from Group 2, 12, 13, or 14 of thePeriodic Table, and 0<m<1. Preferably, M′ is selected from the groupconsisting of Fe, Co, Ni, Mn, Cu, V, Zr, Ti, Cr, and mixtures thereof;more preferably M′ is selected from the group consisting of Fe, Co, Mn,Cu, V, Cr, and mixtures thereof. Preferably, M″ is selected from thegroup consisting of Mg, Ca, Zn, Sr, Pb, Cd, Sn, Ba, Be, Al, and mixturesthereof; more preferably M″ is selected from the group consisting of Mg,Ca, Zn, Ba, Al, and mixtures thereof. Preferably Z comprises F.

[0061] When A is a mixture of lithium and sodium in the formula directlyabove, and the metal or metals M have an average oxidation state of +2,the preferred materials may be written with formula

Li_(1−z)Na_(z)M PO₄

[0062] where z is greater than zero and less than or equal to 1.

[0063] Other preferred embodiments of active materials may be used inthe sodium ion batteries and lithium ion batteries of the invention. Forexample, the active materials may be represented by the formula

A_(a)Li_(e)M_(b)(XY₄)

[0064] where A is Na or a mixture of Na and K, 0.1<a≦1, and a+e≦1;1≦b≦1.5, and XY₄ is as defined above.

[0065] In another embodiment, the active materials have formula:

K_(a)A_(e)M_(b)(PO₄)₃

[0066] where 0.1<a≦6, and a+e≦6, and 1≦b≦3, and where A is sodium,lithium, or a mixture of sodium and lithium.

[0067] In another embodiment, the active materials have formula:

A_(a)Li_(e)M′_(b)M″_(f)(PO₄)₃

[0068] where 0.1<a≦6, and a+e≦6, and 0.1≦b≦3, 1≦(b+f)≦3, and where A issodium, potassium, or a mixture of sodium and potassium. M′ comprises ametal capable of undergoing oxidation to a higher valence state, and M″comprises a non-transition metal selected from groups 2, 3, 12, 13, or14 of the periodic table.

[0069] In yet another embodiment, the active materials have formula:

Na_(a)A_(e)M_(b)(XY₄)₃

[0070] where 0.1<a≦6, and a+e≦6, and 1≦b≦3, with XY₄ comprising amixture of phosphate and silicate represented by P_(1−x) Si_(x) O4,where 0<x≦1. A is lithium, potassium, or a mixture of lithium andpotassium.

[0071] In another embodiment, the active materials have formula:

K_(a)A_(e)M_(b)(XY₄)₃

[0072] where 0.1<a≦6, and a+e≦6, and 1≦b≦3, and XY₄ is a substitutedphosphate group given by P_(1−x)X′_(x)O4, where is X′ is selected fromthe group consisting of As, Sb, Si, Ge, V, S, and mixtures thereof,where 0<x≦1. A is sodium, lithium, or a mixture of sodium and lithium.

[0073] In another embodiment, the active materials are of formula:

A_(a)Li_(e)M_(b)(XY₄)₃

[0074] where 0.1<a≦6, a+e<6, and 1≦b≦3; and XY₄ is an oxygen substitutedgroup selected from the group consisting of X′O_(4−x)Y′_(x),X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is selected fromthe group consisting of P, As, Sb, Si, Ge, V, S, and mixtures thereof;X″ is P, As, Sb, Si, V, Ge or mixtures thereof; Y′ is S, N, or halogen;0<x<3; and 0<y≦4.

[0075] Another preferred embodiment comprises a compound of the formula

A_(a)M¹ _(e)M² _(f)M³ _(g)XY₄,

[0076] wherein

[0077] (a) A is selected from the group consisting of sodium andmixtures of sodium and other alkali metals, and 0<a≦1.5;

[0078] (b) M¹ comprises one or more transition metals, where e>0;

[0079] (c) M² comprises one or more +2 oxidation state non-transitionmetals, where f>0;

[0080] (d) M³ comprises one or more +3 oxidation state non-transitionmetal, where g≧0;

[0081] (e) XY₄ is selected from the group consisting of X′O_(4−x)Y′_(x),X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is P, As, Sb, Si,Ge, V, S, or mixtures thereof; X″ is P, As, Sb, Si, V, Ge, or mixturesthereof; Y′ is S, N, or halogen; 0≦x≦3; and 0<y≦2; and

[0082] wherein e+f+g≦2, and M¹, M², M³, X, Y, a, e, f, g, x, and y areselected so as to maintain electroneutrality of the compound. Inembodiments where XY₄ is PO_(4−x)Y′_(x) and M¹ is a +2 oxidation statetransition metal, a +2e+2f+3g=3−x.

[0083] Preferably, e+f+g=b. In a preferred embodiment 0<(e+f+g)≦2, morepreferably 0.8≦(e+f+g)≦1.5, and even more preferably 0.9≦(e+f+g)≦1,wherein 0<(f+g)<1, preferably 0.01≦(f+g)≦0.5, more preferably0.05≦(f+g)≦0.2, and even more preferably 0.05≦(f+g)≦0.1.

[0084] In a preferred embodiment, A is Na. Preferably, M¹ is at leastone transition metal from Groups 4 to 11 of the Periodic Table; M² is atleast one element from Groups 2, 12, or 14 of the Periodic Table, and M³is a +3 oxidation state element selected from Group 13. Preferably M¹ isselected from the group consisting of Fe, Co, Ni, Mn, Cu, V, Zr, Ti, Cr,and mixtures thereof; more preferably M¹ is a +2 oxidation statetransition metal selected from the group consisting of Fe, Co, Mn, Cu,V, Cr, and mixtures thereof. Preferably M² is selected from the groupconsisting +2 oxidation state non-transition metals and mixturesthereof; more preferably M² is selected from the group consisting of Be,Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg and mixtures thereof. Preferably, M³ is a+3 oxidation state non-transition metal, preferably M³ is selected fromGroup 13, more preferably Sc, Y, La, Ac, B, Al, Ga, In, TI and mixturesthereof. Preferably 0<(f+g)<1, preferably 0.01≦(f+g)≦0.3, morepreferably 0.05≦(f+g)≦0.1. Preferably, 0.01≦f≦0.3, more preferably0.05≦f≦0.1, and even more preferably 0.01≦f≦0.03. Also preferably,0.01≦g≦0.3, more preferably 0.05≦g≦0.1, and even more preferably0.01≦g≦0.03.

[0085] Another preferred embodiment comprises a compound of the formula

Na_(a)Co_(e)Fe_(f)M¹ _(g)M² _(h)M³ _(i)XY₄

[0086] wherein

[0087] (a) 0<a≦2, e>0, and f>0;

[0088] (b) M¹ comprises one or more transition metals, where g≧0;

[0089] (c) M² comprises one or more +2 oxidation state non-transitionmetals, where h≧0;

[0090] (d) M³ comprises one or more +3 oxidation state non-transitionelements, where i≧0; and

[0091] (e) XY₄ is selected from the group consisting of X′O_(4−x)Y′_(x),

[0092] 1. X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′ is P,As, Sb, Si, Ge, V, S, or mixtures thereof; X″ is P, As, Sb, Si, V, Ge,or mixtures thereof; Y′ is S, N, or halogen; 0≦x≦3; and 0<y≦2;

[0093] wherein (e+f+g+h+i)≦2, and M1, M2, M3, X, Y, a, e, f, g, h, i, x,and y are selected so as to maintain electroneutrality of said compound.Preferably, 0.8≦(e+f+g+h+i)≦1.2, more preferably 0.9≦(e+f+g+h+i)≦1.Preferably, e≧0.5, more preferably, e≧0.8. Preferably, 0.01≦f≦0.5, morepreferably, 0.05≦f≦0.15. Preferably, 0.01≦g≦0.5, more preferably,0.05≦g≦0.2. Preferably M¹ is selected from the group consisting of Ti,V, Cr, Mn, Ni, Cu and mixtures thereof. Preferably, M¹ is Mn.

[0094] Preferably, (h+i)>0, more preferably 0.01≦(h+i)≦0.5, morepreferably 0.02≦(h+i)≦0.3. Preferably, 0.01≦h≦0.2, more preferably,0.01≦h≦0.1. Preferably, M² is selected from the group consisting of Be,Mg, Ca, Sr, Ba, and mixtures thereof. More preferably, M² is Mg.Preferably, 0.01≦i≦0.2, more preferably 0.01≦i≦0.1. Preferably, M³ isselected from the group consisting of B, Al, Ga, In and mixturesthereof. More preferably, M³ is Al.

[0095] In one embodiment, XY₄ is PO₄. In another embodiment, XY₄ isPO_(4−x)F_(x), and 0<x≦1, preferably, 0.01≦x≦0.05.

[0096] Another preferred embodiment comprises a compound having anolivine structure. During charge and discharge of the battery, lithiumions are added to, and removed from, the active material preferablywithout substantial changes in the crystal structure of the material.Such materials have sites for the alkali metal (Na), the transitionmetal (M), and the XY₄ (e.g., phosphate) moiety. In some embodiments,all sites of the crystal structure are occupied. In other embodiments,some sites may be unoccupied, depending on, for example, the oxidationstates of the metal (M). Among such preferred compounds are those of theformula

AM(PO_(4−x)Y′_(x))

[0097] wherein

[0098] M is M¹ _(g)M² _(h)M³ _(i)M⁴ _(j), and

[0099] (a) M¹ comprises one or more transition metals;

[0100] (b) M² comprises one or more +2 oxidation state non-transitionmetals;

[0101] (c) M³ comprises one or more +3 oxidation state non-transitionmetals,

[0102] (d) M⁴ comprises one or more +1 oxidation state non-transitionmetals;

[0103] (e) Y′ is halogen; and

[0104] g, >0; h≧0; i≧0; j≧0; (g+h+i+j)≦1. Preferably, g≧0.8, morepreferably, g≧0.9. Preferably, M¹ is a +2 oxidation state transitionmetal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni,Cu and mixtures thereof. More preferably, M¹ is selected from the groupconsisting of Fe, Co, and mixtures thereof.

[0105] Preferably, (h+i)>0.1, more preferably, 0.02≦(h+i)≦0.5, morepreferably, 0.02≦(h+i)≦0.3. Preferably, 0.01≦h≦0.2, more preferably,0.01≦h≦0.1. Preferably, M² is selected from the group consisting of Be,Mg, Ca, Sr, Ba, and mixtures thereof. Preferably, 0.01≦i≦0.2, morepreferably, 0.01≦i≦0.1. Preferably, M³ is Al.

[0106] In one embodiment, j=0. In another embodiment, 0.01≦j≦0.1.Preferably, M⁴ is selected from the group consisting of Li, Na, and K.More preferably, M⁴ is Li.

[0107] In one embodiment, x=0. In another embodiment, 0<x≦1. In such anembodiment, preferably, 0.01≦x≦0.05, and (g+h+i+j)<1. In an embodimentwhere j=0, preferably, (g+h+i)=1−x.

[0108] In a preferred embodiment, M in the above formulas may alsorepresent a vanadyl group, written as VO.

[0109] In another embodiment, the invention provides a battery having acathode and anode, and electrolyte, wherein the cathode contains anelectrochemically active material that can reversibly cycle sodium ions.(The cathode is defined as the electrode at which reduction occursduring discharge. The anode is the electrode at which oxidation occursduring discharge.) In this embodiment, the anode comprises a materialcapable of inserting sodium ions and that can cycle reversibly at aspecific capacity of greater than 100 milliamp hours per gram,preferably greater than 200, and more preferably more than 300 mAh/g. Ina preferred embodiment, the material of the anode comprises a hardcarbon having a particle distribution centered on an average particlediameter of 3-6 micrometers. In another embodiment, the preferred hardcarbon material is characterized by having a d₀₀₂ spacing of greaterthan that of graphite. It is theorized that the greater d₀₀₂ spacing isresponsible in part for the ability of the material to insert andreversibly cycle sodium ions during operation of the battery of theinvention.

[0110] Crystalline graphite, carbon fibers and petroleum coke materialsare generally less preferred anode (negative) electrodes for sodium ioncells. Graphite shows negligible sodium uptake, while petroleum coke andcarbon fiber samples show only relatively low specific capacities(typically in the range 50-100 mAh/g under very low rate conditions). Ina preferred embodiment, the anode of the invention comprises a hardcarbon, such as is commercially available from Osaka Gas Chemical (OsakaGas, Osaka, Japan). The physical properties for this material are shownin Table 3 below.

[0111]FIG. 10 shows the x-ray diffraction data for the Osaka HardCarbon. A Siemens D500 X-ray Diffractometer equipped with Cu K_(α)radiation (λ=1.54056 A) was used for X-ray diffraction (XRD) studies.The broad (002) reflection is clearly centered at 2θ=24.20. Theposition, broadness and relatively low intensity of the (002) reflectionare consistent for a material possessing low crystallinity and verysmall crystallite size. The broadness of the peak is also consistentwith a random distribution of carbon-carbon layers within the material.The expected (004) reflection at approximately 2θ=43.3° is present. Thegeneral features of the x-ray diffraction pattern for the Osaka Gas HardCarbon are fully consistent with those reported by Dahn and co-workers(Electrochim. Acta 38, 1179, (1993)) for some commercially availablehard carbons supplied from an unknown Japanese source, as well as a hardcarbon sample synthesized from polyfurfuryl alcohol. TABLE 3 PhysicalProperties of Commercial Grade Osaka Hard Carbon PROPERTY VALUE Grade96-11-1(4) Mean Particle Size 4.3 μm Ash Content 0.1% Moisture Content0.0% True Specific 1.5 g/cc Gravity

[0112] For carbon material in general, it is the general industrystandard for the values of the interlayer spacing, d₀₀₂, and the latticeconstant, a, to be quoted. The (002) peak arises from the stacking ofthe carbon layers. However, a direct application of the Bragg equation(nλ=2dsinθ) to a broad (002) peak normally yields imprecise values ford₀₀₂. Only when the width of the (002) peak is less than about 2° canits position be reliably used to determine d₀₀₂. The hard carbon of theinvention has such a broad (002) peak. Nevertheless, it can bedetermined from FIG. 12 that the interlayer spacing is larger than isfound in, for example, crystalline graphite samples. It can be theorizedthat the relatively wide interlayer spacing may account for the morefacile insertion of sodium ions into the hard carbon structure, whereasthere is not appreciable uptake of sodium into a graphitic structure.

[0113] The hard carbon of the invention can be further characterized bythe data shown in FIGS. 14 and 15. FIG. 14 shows the particle sizedistribution for a typical hard carbon. It can be seen that the averageparticle size is centered around 4.3 micrometers. FIG. 15 shows ascanning electron micrograph of the Osaka hard carbon.

[0114] Dahn and co-workers (J. Electrochem. Soc. 147, 1271 (2000)) haveproposed a tentative mechanism for sodium insertion into carbonmaterials. They report a structural model having small aromaticfragments of lateral extent around 40 A stacked in a somewhat randomfashion like a house of cards. The random stacking gives rise to smallregions where multiple layers are parallel to each other. The observedsloping potential profile is attributed to insertion of lithium orsodium between parallel or nearly parallel layers. It is said that thepotential decreases with increasing metal content due to the insertionof metal atoms between the layers. Such insertion changes the potentialfor further insertion, it is theorized, because the turbostraticstacking between parallel sheets gives rise to a distribution ofinsertion-site potential.

[0115] Active materials of general formula A_(a)M_(b)(XY₄)_(c)Z_(d) arereadily synthesized by reacting starting materials in a solid statereaction, with or without simultaneous oxidation or reduction of themetal species involved. According to the desired values of a, b, c, andd in the product, starting materials are chosen that contain “a” molesof alkali metal A from all sources, “b” moles of metals M from allsources, “c” moles of phosphate (or other XY₄ species) from all sources,and “d” moles of halide or hydroxide Z, again taking into account allsources. As discussed below, a particular starting material may be thesource of more than one of the components A, M, XY₄, or Z. Alternativelyit is possible to run the reaction with an excess of one or more of thestarting materials. In such a case, the stoichiometry of the productwill be determined by the limiting reagent among the components A, M,XY₄, and Z. Because in such a case at least some of the startingmaterials will be present in the reaction product mixture, it is usuallydesirable to provide exact molar amounts of all the starting materials.

[0116] In still another aspect, the moiety XY₄ of the active materialcomprises a fluoro-substituted phosphate group, represented byPO_(4−x)F_(x), where x is less than or equal to 1, and preferably lessthan or equal to about 0.1. Such groups are formed in the reactionproducts by providing starting materials containing, in addition to thealkali metal and other metals, phosphate in a molar amount equivalent tothe amount necessary to produce a phosphate-containing reaction product.But to make PO_(4−x)F_(x), the starting materials further comprise asource of fluoride in a molar amount sufficient to substitute F in theproduct as shown in the formula. This is generally accomplished byincluding at least “x” moles of F in the starting materials.

[0117] It is preferred to synthesize the active materials of theinvention using stoichiometric amounts of the starting materials, basedon the desired composition of the reaction product expressed by thesubscripts a, b, c, and d above. Alternatively it is possible to run thereaction with a stoichiometric excess of one or more of the startingmaterials. In such a case, the stoichiometry of the product will bedetermined by the limiting reagent among the components. There will alsobe at least some unreacted starting material in the reaction productmixture. Because such impurities in the active materials are generallyundesirable (with the exception of reducing carbon, to be discussedbelow), it is generally preferred to provide relatively exact molaramounts of all the starting materials.

[0118] The sources of components A, M, phosphate (or other XY₄ moiety),and Z may be reacted together in the solid state while heating for atime and temperature sufficient to make a reaction product. The startingmaterials are provided in powder or particulate form. The powders aremixed together with any of a variety of procedures, such as by ballmilling, blending in a mortar and pestle, and the like. Thereafter themixture of powdered starting materials is compressed into a tabletand/or held together with a binder material to form a closely coheringreaction mixture. The reaction mixture is heated in an oven, generallyat a temperature of about 400° C. or greater until a reaction productforms.

[0119] Another means for carrying out the reaction at a lowertemperature is a hydothermal method. In a hydrothermal reaction, thestarting materials are mixed with a small amount of a liquid such aswater, and placed in a pressurized bomb. The reaction temperature islimited to that which can be achieved by heating the liquid water underpressure, and the particular reaction vessel used.

[0120] The reaction may be carried out without redox, or if desired,under reducing or oxidizing conditions. When the reaction is donewithout redox, the oxidation state of the metal or mixed metals in thereaction product is the same as in the starting materials. Oxidizingconditions may be provided by running the reaction in air. Thus, oxygenfrom the air is used to oxidize the starting material containing thetransition metal.

[0121] The reaction may also be carried out with reduction. For example,the reaction may be carried out in a reducing atmosphere such ashydrogen, ammonia, methane, or a mixture of reducing gases.Alternatively, the reduction may be carried out in situ by including inthe reaction mixture a reductant that will participate in the reactionto reduce a metal M, but that will produce by-products that will notinterfere with the active material when used later in an electrode or anelectrochemical cell. The reductant will be described in greater detailbelow. One convenient reductant to use to make the active materials ofthe invention is a reducing carbon. In a preferred embodiment, thereaction is carried out in an inert atmosphere such as argon, nitrogen,or carbon dioxide. Such reducing carbon is conveniently provided byelemental carbon, or by an organic material that can decompose under thereaction conditions to form elemental carbon or a similar carboncontaining species that has reducing power. Such organic materialsinclude, without limitation, glycerol, starch, sugars, cokes, andorganic polymers which carbonize or pyrolize under the reactionconditions to produce a reducing form of carbon. A preferred source ofreducing carbon is elemental carbon.

[0122] Sources of alkali metal include any of a number of salts or ioniccompounds of lithium, sodium, potassium, rubidium or cesium. Lithium,sodium, and potassium compounds are preferred, with lithium beingparticularly preferred. Preferably, the alkali metal source is providedin powder or particulate form. A wide range of such materials is wellknown in the field of inorganic chemistry. Examples include the lithium,sodium, and/or potassium fluorides, chlorides, bromides, iodides,nitrates, nitrites, sulfates, hydrogen sulfates, sulfites, bisulfites,carbonates, bicarbonates, borates, phosphates, hydrogen ammoniumphosphates, dihydrogen ammonium phosphates, silicates, antimonates,arsenates, germinates, oxides, acetates, oxalates, and the like.Hydrates of the above compounds may also be used, as well as mixtures.In particular, the mixtures may contain more than one alkali metal sothat a mixed alkali metal active material will be produced in thereaction.

[0123] Sources of metals M, M¹, M², M³, and M⁴ include salts orcompounds of any of the transition metals, alkaline earth metals, orlanthanide metals, as well as of non-transition elements such asaluminum, gallium, indium, thallium, tin, lead, and bismuth. The metalsalts or compounds include fluorides, chlorides, bromides, iodides,nitrates, nitrites, sulfates, hydrogen sulfates, sulfites, bisulfites,carbonates, bicarbonates, borates, phosphates, hydrogen ammoniumphosphates, dihydrogen ammonium phosphates, silicates, antimonates,arsenates, germanates, oxides, hydroxides, acetates, oxalates, and thelike. Hydrates may also be used. The metal M in the starting materialmay have any oxidation state, depending the oxidation state required inthe desired product and the oxidizing or reducing conditionscontemplated, as discussed below. In particular, the cobalt and iron ofthe active materials may be provided by starting materials with Co⁺²,Co⁺³, Fe⁺², or Fe⁺³. The metal sources are chosen so that at least onemetal in the final reaction product is capable of being in an oxidationstate higher than it is in the reaction product. In a preferredembodiment, the metal sources also include a +2 non-transition metal.Also preferably, at least one metal source is a source of a +3non-transition element.

[0124] Sources of the desired starting material anions, such asphosphates, are provided by a number of salts or compounds containingpositively charged cations in addition to a source of phosphate (orother XY₄ species). Such cations include metal ions such as the alkalimetals, alkaline metals, transition metals, or other non-transitionelements, as well as complex cations such as ammonium or quaternaryammonium. The phosphate anion in such compounds may be phosphate,hydrogen ammonium phosphate, or dihydrogen ammonium phosphate. As withthe alkali metal source and metal source discussed above, the phosphateor other XY₄ species starting materials are preferably provided inparticulate or powder form. Hydrates of any of the above may be used, ascan mixtures of the above.

[0125] As noted above, the active materials A_(a) M_(b) XY₄ of theinvention can contain a mixture of alkali metals A, a mixture of metalsM, and a phosphate group representative of the XY₄ group in the formula.In another aspect of the invention, the phosphate group can becompletely or partially substituted by a number of other XY₄ moieties,which will also be referred to as “phosphate replacements” or “modifiedphosphates.” Thus, active materials are provided according to theinvention wherein the XY₄ moiety is a phosphate group that is completelyor partially replaced by such moieties as sulfate (SO₄)²⁻,monofluoromonophosphate, (PO₃F)²⁻, difluoromonophosphate (PO₂F)²⁻,silicate (SiO₄)⁴⁻, arsenate, antimonate, and germanate. Analogues of theabove oxygenate anions where some or all of the oxygen is replaced bysulfur are also useful in the active materials of the invention, withthe exception that the sulfate group may not be completely substitutedwith sulfur. For example thiomonophosphates may also be used as acomplete or partial replacement for phosphate in the active materials ofthe invention. Such thiomonophosphates include the anions (PO₃S)³⁻,(PO₂S₂)³⁻, (POS₃)³⁻, and (PS₄)³⁻. They are most conveniently availableas the sodium, lithium, or potassium derivative.

[0126] To synthesize the active materials containing the modifiedphosphate moieties, it is usually possible to substitute all orpreferably only part of the phosphate compounds discussed above with asource of the replacement anion. The replacement is considered on astoichiometric basis. Starting materials providing the source of thereplacement anions are provided along with the other starting materialsas discussed above. Synthesis of the active materials containing themodified phosphate groups proceeds as discussed above, either withoutredox or under oxidizing or reducing conditions. As was the case withthe phosphate compounds, the compound containing the modified orreplacement phosphate group or groups may also be a source of othercomponents of the active materials. For example, the alkali metal and/orany of the other metals may be a part of the modified phosphatecompound.

[0127] Non-limiting examples of sources of monofluoromonophosphatesinclude Na₂PO₃F, K₂PO₃F, (NH₄)₂PO₃F.H₂O, LiNaPO₃F.H₂O, LiKPO₃F,LiNH₄PO₃F, NaNH₄PO₃F, NaK₃(PO₃F)₂ and CaPO₃F.2H₂O. Representativeexamples of sources of difluoromonophosphate compounds include, withoutlimitation, NH₄PO₂F₂, NaPO₂F₂, KPO₂F₂, Al(PO₂F₂)₃, and Fe(PO₂F₂)₃.

[0128] When it is desired to partially or completely replace phosphorousin the active materials with silicon, it is possible to use a widevariety of silicates and other silicon containing compounds. Thus,useful sources of silicon in the active materials of the inventioninclude orthosilicates, pyrosilicates, cyclic silicate anions such as(Si₃O₉)⁶⁻, (Si₆O₁₈)¹²⁻ and the like, and pyrocenes represented by theformula [(SiO₃)²⁻]_(n), for example LiAl(SiO₃)₂. Silica or SiO₂ may alsobe used. Partial substitution of silicate for phosphate is illustratedin Example 4.

[0129] Representative arsenate compounds that may be used to prepare theactive materials of the invention include H₃AsO₄ and salts of the anions[H₂AsO₄]⁻ and [HAsO₄]²⁻. Sources of antimonate in the active materialscan be provided by antimony-containing materials such as Sb₂O₅,M^(I)SbO₃ where M^(I) is a metal having oxidation state +1, M^(III)SbO₄where M^(III) is a metal having an oxidation state of +3, andM^(II)Sb₂O₇ where M^(II) is a metal having an oxidation state of +2.Additional sources of antimonate include compounds such as Li₃SbO₄,NH₄H₂SbO₄, and other alkali metal and/or ammonium mixed salts of the[SbO₄]³⁻ anion.

[0130] Sources of sulfate compounds that can be used to partially orcompletely replace phosphorous in the active materials with sulfurinclude alkali metal and transition metal sulfates and bisulfates aswell as mixed metal sulfates such as (NH₄)₂Fe(SO₄)₂, NH₄Fe(SO₄)₂ and thelike. Finally, when it is desired to replace part or all of thephosphorous in the active materials with germanium, a germaniumcontaining compound such as GeO₂ may be used.

[0131] To prepare the active materials containing the modified phosphategroups, it generally suffices to choose the stoichiometry of thestarting materials based on the desired stoichiometry of the modifiedphosphate groups in the final product and react the starting materialstogether according to the procedures described above with respect to thephosphate materials. Naturally, partial or complete substitution of thephosphate group with any of the above modified or replacement phosphategroups will entail a recalculation of the stoichiometry of the requiredstarting materials.

[0132] A starting material may provide more than one of the componentsA, M, and XY₄, as is evident in the list above. In various embodimentsof the invention, starting materials are provided that combine, forexample, the metal and the phosphate, thus requiring only the alkalimetal to be added. In one embodiment, a starting material is providedthat contains alkali metal, metal, and phosphate. As a general rule,there is flexibility to select starting materials containing any of thecomponents of alkali metal A, metal M, and phosphate (or other XY₄moiety), depending on availability. Combinations of starting materialsproviding each of the components may also be used.

[0133] In general, any anion may be combined with the alkali metalcation to provide the alkali metal source starting material, or with ametal M cation to provide a metal starting material. Likewise, anycation may be combined with the halide or hydroxide anion to provide thesource of Z component starting material, and any cation may be used ascounterion to the phosphate or similar XY₄ component. It is preferred,however, to select starting materials with counterions that give rise tothe formation of volatile by-products during the solid state reaction.Thus, it is desirable to choose ammonium salts, carbonates, oxides,hydroxides, and the like where possible. Starting materials with thesecounterions tend to form volatile by-products such as water, ammonia,and carbon dioxide, which can be readily removed from the reactionmixture.

[0134] As noted above, the reactions may be carried out withoutreduction, or in the presence of a reductant. In one aspect, thereductant, which provides reducing power for the reactions, may beprovided in the form of a reducing carbon by including a source ofelemental carbon along with the other particulate starting materials. Inthis case, the reducing power is provided by simultaneous oxidation ofcarbon to either carbon monoxide or carbon dioxide.

[0135] The starting materials containing transition metal compounds aremixed together with carbon, which is included in an amount sufficient toreduce the metal ion of one or more of the metal-containing startingmaterials without full reduction to an elemental metal state. Excessquantities of one or more starting materials (for example, about a 5 to10% excess) may be used to enhance product quality. An excess of carbon,remaining after the reaction, functions as a conductive constituent inthe ultimate electrode formulation. This is an advantage since suchremaining carbon is very intimately mixed with the product activematerial. Accordingly, large quantities of excess carbon, on the orderof 100% excess carbon or greater are useable in the process. In apreferred embodiment, the carbon present during compound formation isintimately dispersed throughout the precursor and product. This providesmany advantages, including the enhanced conductivity of the product. Ina preferred embodiment, the presence of carbon particles in the startingmaterials is also provides nucleation sites for the production of theproduct crystals.

[0136] Alternatively or in addition, the source of reducing carbon maybe provided by an organic material. The organic material ischaracterized as containing carbon and at least one other element,preferably hydrogen. The organic material generally forms adecomposition product, referred to herein as a carbonaceous material,upon heating under the conditions of the reaction. Without being boundby theory, representative decomposition processes that can lead to theformation of the carbonaceous material include pyrolization,carbonization, coking, destructive distillation, and the like. Theseprocess names, as well as the term thermal decomposition, are usedinterchangeably in this application to refer to the process by which adecomposition product capable of acting as a reductant is formed uponheating of a reaction mixture containing an organic material.

[0137] A typical decomposition product contains carbonaceous material.During reaction in a preferred embodiment, at least a portion of thecarbonaceous material formed participates as a reductant. That portionthat participates as reductant may form a volatile by-product such asdiscussed below. Any volatile by-product formed tends to escape from thereaction mixture so that it is not incorporated into the reactionproduct.

[0138] Although the invention is understood not to be limited as to themechanism of action of the organic precursor material, it believed thatthe carbonaceous material formed from decomposition of the organicmaterial provides reducing power similar to that provided by elementalcarbon discussed above. For example, the carbonaceous material mayproduce carbon monoxide or carbon dioxide, depending on the temperatureof the reaction.

[0139] In a preferred embodiment, some of the organic material providingreducing power is oxidized to a non-volatile component, such as forexample, oxygen-containing carbon materials such as alcohols, ketones,aldehydes, esters, and carboxylic acids and anhydrides. Suchnon-volatile by-products, as well as any carbonaceous material that doesnot participate as reductant (for example, any present in stoichiometricexcess or any that does not otherwise react) will tend to remain in thereaction mixture along with the other reaction products, but will not besignificantly covalently incorporated.

[0140] The carbonaceous material prepared by heating the organicprecursor material will preferably be enriched in carbon relative to themole percent carbon present in the organic material. The carbonaceousmaterial preferably contains from about 50 up to about 100 mole percentcarbon.

[0141] While in some embodiments the organic precursor material forms acarbonaceous decomposition product that acts as a reductant as discussedabove with respect to elemental carbon, in other embodiments a portionof the organic material participates as reductant without firstundergoing a decomposition. The invention is not limited by the exactmechanism or mechanisms of the underlying reduction processes.

[0142] As with elemental carbon, reactions with the organic precursormaterial are conveniently carried out by combining starting materialsand heating. The starting materials include at least one transitionmetal compound as noted above. For convenience, it is preferred to carryout the decomposition of the organic material and the reduction of atransition metal in one step. In this embodiment, the organic materialdecomposes in the presence of the transition metal compound to form adecomposition product capable of acting as a reductant, which reactswith the transition metal compound to form a reduced transition metalcompound. In another embodiment, the organic material may be decomposedin a separate step to form a decomposition product. The decompositionproduct may then be combined with a transition metal compound to form amixture. The mixture may then be heated for a time and at a temperaturesufficient to form a reaction product comprising a reduced transitionmetal compound.

[0143] The organic precursor material may be any organic materialcapable of undergoing pyrolysis or carbonization, or any otherdecomposition process that leads to a carbonaceous material rich incarbon. Such precursors include in general any organic material, i.e.,compounds characterized by containing carbon and at least one otherelement. Although the organic material may be a perhalo compoundcontaining essentially no carbon-hydrogen bonds, typically the organicmaterials contain carbon and hydrogen. Other elements, such as halogens,oxygen, nitrogen, phosphorus, and sulfur, may be present in the organicmaterial, as long as they do not significantly interfere with thedecomposition process or otherwise prevent the reductions from beingcarried out. Precursors include organic hydrocarbons, alcohols, esters,ketones, aldehydes, carboxylic acids, sulfonates, and ethers. Preferredprecursors include the above species containing aromatic rings,especially the aromatic hydrocarbons such as tars, pitches, and otherpetroleum products or fractions. As used here, hydrocarbon refers to anorganic compound made up of carbon and hydrogen, and containing nosignificant amounts of other elements. Hydrocarbons may containimpurities having some heteroatoms. Such impurities might result, forexample, from partial oxidation of a hydrocarbon or incompleteseparation of a hydrocarbon from a reaction mixture or natural sourcesuch as petroleum.

[0144] Other organic precursor materials include sugars and othercarbohydrates, including derivatives and polymers. Examples of polymersinclude starch, cellulose, and their ether or ester derivatives. Otherderivatives include the partially reduced and partially oxidizedcarbohydrates discussed below. On heating, carbohydrates readilydecompose to form carbon and water. The term carbohydrates as used hereencompasses the D-, L-, and DL-forms, as well as mixtures, and includesmaterial from natural or synthetic sources.

[0145] In one sense as used in the invention, carbohydrates are organicmaterials that can be written with molecular formula (C)_(m) (H₂O)_(n),where m and n are integers. For simple hexose or pentose sugars, m and nare equal to each other. Examples of hexoses of formula C₆H₁₂O₆ includeallose, altose, glucose, mannose, gulose, inose, galactose, talose,sorbose, tagatose, and fructose. Pentoses of formula C₅H₁₀O₅ includeribose, arabinose, and xylose. Tetroses include erythrose and threose,while glyceric aldehyde is a triose. Other carbohydrates include thetwo-ring sugars (disaccharides) of general formula C₁₂H₂₂O₁₁. Examplesinclude sucrose, maltose, lactose, trehalose, gentiobiose, cellobiose,and melibiose. Three-ring (trisaccharides such as raffinose) and higheroligomeric and polymer carbohydrates may also be used. Examples includestarch and cellulose. As noted above, the carbohydrates readilydecompose to carbon and water when heated to a sufficiently hightemperature. The water of decomposition tends to turn to steam under thereaction conditions and volatilize.

[0146] It will be appreciated that other materials will also tend toreadily decompose to H₂O and a material very rich in carbon. Suchmaterials are also intended to be included in the term “carbohydrate” asused in the invention. Such materials include slightly reducedcarbohydrates such as glycerol, sorbitol, mannitol, iditol, dulcitol,talitol, arabitol, xylitol, and adonitol, as well as “slightly oxidized”carbohydrates such as gluconic, mannonic, glucuronic, galacturonic,mannuronic, saccharic, manosaccharic, ido-saccharic, mucic, talo-mucic,and allo-mucic acids. The formula of the slightly oxidized and theslightly reduced carbohydrates is similar to that of the carbohydrates.

[0147] A preferred carbohydrate is sucrose. Under the reactionconditions, sucrose melts at about 150-180° C. Preferably, the liquidmelt tends to distribute itself among the starting materials. Attemperatures above about 450° C., sucrose and other carbohydratesdecompose to form carbon and water. The as-decomposed carbon powder isin the form of fresh amorphous fine particles with high surface area andhigh reactivity.

[0148] The organic precursor material may also be an organic polymer.Organic polymers include polyolefins such as polyethylene andpolypropylene, butadiene polymers, isoprene polymers, vinyl alcoholpolymers, furfuryl alcohol polymers, styrene polymers includingpolystyrene, polystyrene-polybutadiene and the like, divinylbenzenepolymers, naphthalene polymers, phenol condensation products includingthose obtained by reaction with aldehyde, polyacrylonitrile, polyvinylacetate, as well as cellulose starch and esters and ethers thereofdescribed above.

[0149] In some embodiments, the organic precursor material is a solidavailable in particulate form. Particulate materials may be combinedwith the other particulate starting materials and reacted by heatingaccording to the methods described above.

[0150] In other embodiments, the organic precursor material may be aliquid. In such cases, the liquid precursor material is combined withthe other particulate starting materials to form a mixture. The mixtureis heated, whereupon the organic material forms a carbonaceous materialin situ. The reaction proceeds with carbothermal reduction. The liquidprecursor materials may also advantageously serve or function as abinder in the starting material mixture as noted above.

[0151] Reducing carbon is preferably used in the reactions instoichiometric excess. To calculate relative molar amounts of reducingcarbon, it is convenient to use an “equivalent” weight of the reducingcarbon, defined as the weight per gram-mole of carbon atom. Forelemental carbons such as carbon black, graphite, and the like, theequivalent weight is about 12 g/equivalent. For other organic materials,the equivalent weight per gram-mole of carbon atoms is higher. Forexample, hydrocarbons have an equivalent weight of about 14g/equivalent. Examples of hydrocarbons include aliphatic, alicyclic, andaromatic hydrocarbons, as well as polymers containing predominantly orentirely carbon and hydrogen in the polymer chain. Such polymers includepolyolefins and aromatic polymers and copolymers, includingpolyethylenes, polypropylenes, polystyrenes, polybutadienes, and thelike. Depending on the degree of unsaturation, the equivalent weight maybe slightly above or below 14.

[0152] For organic materials having elements other than carbon andhydrogen, the equivalent weight for the purpose of calculating astoichiometric quantity to be used in the reactions is generally higherthan 14. For example, in carbohydrates it is about 30 g/equivalent.Examples of carbohydrates include sugars such as glucose, fructose, andsucrose, as well as polymers such as cellulose and starch.

[0153] Although the reactions may be carried out in oxygen or air, theheating is preferably conducted under an essentially non-oxidizingatmosphere. The atmosphere is essentially non-oxidizing so as not tointerfere with the reduction reactions taking place. An essentiallynon-oxidizing atmosphere can be achieved through the use of vacuum, orthrough the use of inert gases such as argon, nitrogen, and the like.Although oxidizing gas (such as oxygen or air), may be present, itshould not be at so great a concentration that it interferes with thecarbothermal reduction or lowers the quality of the reaction product. Itis believed that any oxidizing gas present will tend to react with thereducing carbon and lower the availability of the carbon forparticipation in the reaction. To some extent, such a contingency can beanticipated and accommodated by providing an appropriate excess ofreducing carbon as a starting material. Nevertheless, it is generallypreferred to carry out the carbothermal reduction in an atmospherecontaining as little oxidizing gas as practical.

[0154] In a preferred embodiment, reduction is carried out in a reducingatmosphere in the presence of a reductant as discussed above. The term“reducing atmosphere” as used herein means a gas or mixture of gasesthat is capable of providing reducing power for a reaction that iscarried out in the atmosphere. Reducing atmospheres preferably containone or more so-called reducing gases. Examples of reducing gases includehydrogen, carbon monoxide, methane, and ammonia, as well as mixturesthereof. Reducing atmospheres also preferably have little or nooxidizing gases such as air or oxygen. If any oxidizing gas is presentin the reducing atmosphere, it is preferably present at a level lowenough that it does not significantly interfere with reductionprocesses.

[0155] The stoichiometry of the reduction can be selected along with therelative stoichiometric amounts of the starting components A, M, PO₄ (orother XY₄ moiety), and Z. It is usually easier to provide the reducingagent in stoichiometric excess and remove the excess, if desired, afterthe reaction. In the case of the reducing gases and the use of reducingcarbon such as elemental carbon or an organic material, any excessreducing agent does not present a problem. In the former case, the gasis volatile and is easily separated from the reaction mixture, while inthe latter, the excess carbon in the reaction product does not harm theproperties of the active material, particularly in embodiments wherecarbon is added to the active material to form an electrode material foruse in the electrochemical cells and batteries of the invention.Conveniently also, the by-products carbon monoxide or carbon dioxide (inthe case of carbon) or water (in the case of hydrogen) are readilyremoved from the reaction mixture.

[0156] When using a reducing atmosphere, it is difficult to provide lessthan an excess of reducing gas such as hydrogen. Under such as asituation, it is preferred to control the stoichiometry of the reactionby the other limiting reagents. Alternatively the reduction may becarried out in the presence of reducing carbon such as elemental carbon.Experimentally, it would be possible to use precise amounts of reductantcarbon as illustrated in the table for the case of reductant hydrogen tomake products of a chosen stoichiometry. However, it is preferred tocarry out the carbothermal reduction in a molar excess of carbon. Aswith the reducing atmosphere, this is easier to do experimentally, andit leads to a product with excess carbon dispersed into the reactionproduct, which as noted above provides a useful active electrodematerial.

[0157] Before reacting the mixture of starting materials, the particlesof the starting materials are intermingled. Preferably, the startingmaterials are in particulate form, and the intermingling results in anessentially homogeneous powder mixture of the precursors. In oneembodiment, the precursor powders are dry-mixed using, for example, aball mill. Then the mixed powders are pressed into pellets. In anotherembodiment, the precursor powders are mixed with a binder. The binder ispreferably selected so as to not inhibit reaction between particles ofthe powders. Preferred binders decompose or evaporate at a temperatureless than the reaction temperature. Examples include mineral oils,glycerol, and polymers that decompose or carbonize to form a carbonresidue before the reaction starts, or that evaporate before thereaction starts. In one embodiment, the binders used to hold the solidparticles also function as sources of reducing carbon, as describedabove. In still another embodiment, intermingling is accomplished byforming a wet mixture using a volatile solvent and then the intermingledparticles are pressed together in pellet form to provide goodgrain-to-grain contact.

[0158] The mixture of starting materials is heated for a time and at atemperature sufficient to form an inorganic transition metal compoundreaction product. If the starting materials include a reducing agent,the reaction product is a transition metal compound having at least onetransition metal in a lower oxidation state relative to its oxidationstate in the starting materials.

[0159] Preferably, the particulate starting materials are heated to atemperature below the melting point of the starting materials.Preferably, at least a portion of the starting material remains in thesolid state during the reaction.

[0160] The temperature should preferably be about 400° C. or greater,and desirably about 450° C. or greater, and preferably about 500° C. orgreater, and generally will proceed at a faster rate at highertemperatures. The various reactions involve production of CO or CO₂ asan effluent gas. The equilibrium at higher temperature favors COformation. Some of the reactions are more desirably conducted attemperatures greater than about 600° C.; most desirably greater thanabout 650° C.; preferably about 700° C. or greater; more preferablyabout 750° C. or greater. Suitable ranges for many reactions are fromabout 700 to about 950° C., or from about 700 to about 800° C.

[0161] Generally, the higher temperature reactions produce CO effluentand the stoichiometry requires more carbon be used than the case whereCO₂ effluent is produced at lower temperature. This is because thereducing effect of the C to CO₂ reaction is greater than the C to COreaction. The C to CO₂ reaction involves an increase in carbon oxidationstate of +4 (from 0 to 4) and the C to CO reaction involves an increasein carbon oxidation state of +2 (from ground state zero to 2). Here,higher temperature generally refers to a range of about 650° C. to about1000° C. and lower temperature refers to up to about 650° C.Temperatures higher than about 1200° C. are not thought to be needed.

[0162] In one embodiment, the methods of this invention utilize thereducing capabilities of carbon in a unique and controlled manner toproduce desired products having structure and alkali metal contentsuitable for use as electrode active materials. The advantages are atleast in part achieved by the reductant, carbon, having an oxide whosefree energy of formation becomes more negative as temperature increases.Such oxide of carbon is more stable at high temperature than at lowtemperature. This feature is used to produce products having one or moremetal ions in a reduced oxidation state relative to the precursor metalion oxidation state. The method utilizes an effective combination ofquantity of carbon, time and temperature to produce new products and toproduce known products in a new way.

[0163] Referring back to the discussion of temperature, at about 700° C.both the carbon to carbon monoxide and the carbon to carbon dioxidereactions are occurring. At closer to about 600° C. the C to CO₂reaction is the dominant reaction. At closer to about 800° C. the C toCO reaction is dominant. Since the reducing effect of the C to CO₂reaction is greater, the result is that less carbon is needed per atomicunit of metal to be reduced. In the case of carbon to carbon monoxide,each atomic unit of carbon is oxidized from ground state zero to plus 2.Thus, for each atomic unit of metal ion (M) which is being reduced byone oxidation state, one half atomic unit of carbon is required. In thecase of the carbon to carbon dioxide reaction, one quarter atomic unitof carbon is stoichiometrically required for each atomic unit of metalion (M) which is reduced by one oxidation state, because carbon goesfrom ground state zero to a plus 4 oxidation state. These samerelationships apply for each such metal ion being reduced and for eachunit reduction in oxidation state desired.

[0164] The starting materials may be heated at ramp rates from afraction of a degree up to about 10° C. per minute. Higher or lower ramprates may be chosen depending on the available equipment, desiredturnaround, and other factors. It is also possible to place the startingmaterials directly into a pre-heated oven. Once the desired reactiontemperature is attained, the reactants (starting materials) are held atthe reaction temperature for a time sufficient for reaction to occur.Typically the reaction is carried out for several hours at the finalreaction temperature. The heating is preferably conducted undernon-oxidizing or inert gas such as argon or vacuum, or in the presenceof a reducing atmosphere.

[0165] After reaction, the products are preferably cooled from theelevated temperature to ambient (room) temperature (i.e., about 10° C.to about 40° C.). The rate of cooling may vary according to a number offactors including those discussed above for heating rates. For example,the cooling may be conducted at a rate similar to the earlier ramp rate.Such a cooling rate has been found to be adequate to achieve the desiredstructure of the final product. It is also possible to quench theproducts to achieve a higher cooling rate, for example on the order ofabout 100° C./minute.

[0166] The general aspects of the above synthesis routes are applicableto a variety of starting materials. The metal compounds may be reducedin the presence of a reducing agent, such as hydrogen or carbon. Thesame considerations apply to other metal and phosphate containingstarting materials. The thermodynamic considerations such as ease ofreduction of the selected starting materials, the reaction kinetics, andthe melting point of the salts will cause adjustment in the generalprocedure, such as the amount of reducing agent, the temperature of thereaction, and the dwell time.

[0167] The method includes reacting a lithium containing compound(lithium carbonate, Li₂CO₃), a metal containing compound having aphosphate group (for example, nickel phosphate, Ni₃(PO₄)₂.xH₂O, whichusually has more than one mole of water), and a phosphoric acidderivative (such as a diammonium hydrogen phosphate, DAHP). The powdersare pre-mixed with a mortar and pestle until uniformly dispersed,although various methods of mixing may be used. The mixed powders of thestarting materials are pressed into pellets. The first stage reaction isconducted by heating the pellets in an oven at a preferred heating rateto an elevated temperature, and held at such elevated temperature forseveral hours. A preferred ramp rate of about 2° C./minute is used toheat to a preferable temperature of about 800° C. Although in manyinstances a heating rate is desirable for a reaction, it is not alwaysnecessary for the success of the reaction. The reaction is carried outunder a flowing air atmosphere (e.g., when M is Ni or Co), although thereaction could be carried out in an inert atmosphere such as N₂ or Ar(when M is Fe). The flow rate will depend on the size of the oven andthe quantity needed to maintain the atmosphere. The reaction mixture isheld at the elevated temperature for a time sufficient for the reactionproduct to be formed. The pellets are then allowed to cool to ambienttemperature. The rate at which a sample is cooled may vary.

[0168] Electrodes:

[0169] The present invention also provides electrodes comprising anelectrode active material of the present invention. In a preferredembodiment, the electrodes of the present invention comprise anelectrode active material of this invention, a binder; and anelectrically conductive carbonaceous material.

[0170] In a preferred embodiment, the electrodes of this inventioncomprise:

[0171] (a) from about 25% to about 95%, more preferably from about 50%to about 90%, active material;

[0172] (b) from about 2% to about 95% electrically conductive material(e.g., carbon black); and

[0173] (c) from about 3% to about 20% binder chosen to hold allparticulate materials in contact with one another without degradingionic conductivity.

[0174] (Unless stated otherwise, all percentages herein are by weight.)Cathodes of this invention preferably comprise from about 50% to about90% of active material, about 5% to about 30% of the electricallyconductive material, and the balance comprising binder. Anodes of thisinvention preferably comprise from about 50% to about 95% by weight ofthe electrically conductive material (e.g., a preferred graphite), withthe balance comprising binder.

[0175] Electrically conductive materials among those useful hereininclude carbon black, graphite, powdered nickel, metal particles,conductive polymers (e.g., characterized by a conjugated network ofdouble bonds like polypyrrole and polyacetylene), and mixtures thereof.Binders useful herein preferably comprise a polymeric material andextractable plasticizer suitable for forming a bound porous composite.Preferred binders include halogenated hydrocarbon polymers (such aspoly(vinylidene chloride) and poly((dichloro-1, 4-phenylene)ethylene),fluorinated urethanes, fluorinated epoxides, fluorinated acrylics,copolymers of halogenated hydrocarbon polymers, epoxides, ethylenepropylene diamine termonomer (EPDM), ethylene propylene diaminetermonomer (EPDM), polyvinylidene difluoride (PVDF), hexafluoropropylene(HFP), ethylene acrylic acid copolymer (EAA), ethylene vinyl acetatecopolymer (EVA), EAA/EVA copolymers, PVDF/HFP copolymers, and mixturesthereof.

[0176] In a preferred process for making an electrode, the electrodeactive material is mixed into a slurry with a polymeric binder compound,a solvent, a plasticizer, and optionally the electroconductive material.The active material slurry is appropriately agitated, and then thinlyapplied to a substrate via a doctor blade. The substrate can be aremovable substrate or a functional substrate, such as a currentcollector (for example, a metallic grid or mesh layer) attached to oneside of the electrode film. In one embodiment, heat or radiation isapplied to evaporate the solvent from the electrode film, leaving asolid residue. The electrode film is further consolidated, where heatand pressure are applied to the film to sinter and calendar it. Inanother embodiment, the film may be air-dried at moderate temperature toyield self-supporting films of copolymer composition. If the substrateis of a removable type it is removed from the electrode film, andfurther laminated to a current collector. With either type of substrateit may be necessary to extract the remaining plasticizer prior toincorporation into the battery cell.

[0177] Batteries:

[0178] The batteries of the present invention comprise:

[0179] (d) a first electrode comprising an active material of thepresent invention;

[0180] (e) a second electrode which is a counter-electrode to said firstelectrode; and

[0181] (f) an electrolyte between said electrodes.

[0182] The electrode active material of this invention may comprise theanode, the cathode, or both. Preferably, the electrode active materialcomprises the cathode.

[0183] The active material of the second, counter-electrode is anymaterial compatible with the electrode active material of thisinvention. In embodiments where the electrode active material comprisesthe cathode, the anode may comprise any of a variety of compatibleanodic materials well known in the art, including lithium, lithiumalloys, such as alloys of lithium with aluminum, mercury, manganese,iron, zinc, and intercalation based anodes such as those employingcarbon, tungsten oxides, and mixtures thereof. In a preferredembodiment, the anode comprises:

[0184] (g) from about 0% to about 95%, preferably from about 25% toabout 95%, more preferably from about 50% to about 90%, of an insertionmaterial;

[0185] (h) from about 2% to about 95% electrically conductive material(e.g., carbon black); and

[0186] (i) from about 3% to about 20% binder chosen to hold allparticulate materials in contact with one another without degradingionic conductivity.

[0187] In a particularly preferred embodiment, the anode comprises fromabout 50% to about 90% of an insertion material selected from the groupactive material from the group consisting of metal oxides (particularlytransition metal oxides), metal chalcogenides, and mixtures thereof. Inanother preferred embodiment, the anode does not contain an insertionactive, but the electrically conductive material comprises an insertionmatrix comprising carbon, graphite, cokes, mesocarbons and mixturesthereof. One preferred anode intercalation material is carbon, such ascoke or graphite, which is capable of forming the compound Li_(x)C.Insertion anodes among those useful herein are described in U.S. Pat.No. 5,700,298, Shi et al., issued Dec. 23, 1997; U.S. Pat. No.5,712,059, Barker et al., issued Jan. 27, 1998; U.S. Pat. No. 5,830,602,Barker et al., issued Nov. 3, 1998; and U.S. Pat. No. 6,103,419, Saidiet al., issued Aug. 15, 2000; all of which are incorporated by referenceherein.

[0188] In embodiments where the electrode active material comprises theanode, the cathode preferably comprises:

[0189] (j) from about 25% to about 95%, more preferably from about 50%to about 90%, active material;

[0190] (k) from about 2% to about 95% electrically conductive material(e.g., carbon black); and

[0191] (l) from about 3% to about 20% binder chosen to hold allparticulate materials in contact with one another without degradingionic conductivity.

[0192] Active materials useful in such cathodes include electrode activematerials of this invention, as well as metal oxides (particularlytransition metal oxides), metal chalcogenides, and mixtures thereof.Other active materials include lithiated transition metal oxides such asLiCoO₂, LiNiO₂, and mixed transition metal oxides such asLiCo_(1−m)Ni_(m)O₂, where 0<m<1. Another preferred active materialincludes lithiated spinel active materials exemplified by compositionshaving a structure of LiMn₂O₄, as well as surface treated spinels suchas disclosed in U.S. Pat. No. 6,183,718, Barker et al., issued Feb. 6,2001, incorporated by reference herein. Blends of two or more of any ofthe above active materials may also be used. The cathode mayalternatively further comprise a basic compound to protect againstelectrode degradation as described in U.S. Pat. No. 5,869,207, issuedFeb. 9, 1999, incorporated by reference herein.

[0193] The batteries of this invention also comprise a suitableelectrolyte that provides a physical separation but allows transfer ofions between the cathode and anode. The electrolyte is preferably amaterial that exhibits high ionic conductivity, as well as havinginsular properties to prevent self-discharging during storage. Theelectrolyte can be either a liquid or a solid. A liquid electrolytecomprises a solvent and an alkali metal salt that together form antonically conducting liquid. So called “solid electrolytes” contain inaddition a matrix material that is used to separate the electrodes.

[0194] One preferred embodiment is a solid polymeric electrolyte, madeup of a solid polymeric matrix and a salt homogeneously dispersed via asolvent in the matrix. Suitable solid polymeric matrices include thosewell known in the art and include solid matrices formed from organicpolymers, inorganic polymers or a solid matrix-forming monomer and frompartial polymers of a solid matrix forming monomer.

[0195] In another variation, the polymer, solvent and salt together forma gel which maintains the electrodes spaced apart and provides the ionicconductivity between electrodes. In still another variation, theseparation between electrodes is provided by a glass fiber mat or othermatrix material and the solvent and salt penetrate voids in the matrix.

[0196] The electrolytes of the present invention comprise an saltdissolved in a mixture of an alkylene carbonate and a cyclic ester.Preferably, the salt of the electrolyte is a lithium or sodium salt.Such salts among those useful herein include LiAsF₆, LiPF₆, LiClO₄,LiB(C₆H₅)₄, LiAlCl₄, LiBr, LiBF₄, and mixtures thereof, as well assodium analogs, with the less toxic salts being preferable. The saltcontent is preferably from about 5% to about 65%, preferably from about8% to about 35% (by weight of electrolyte). A preferred salt is LiBF₄.In a preferred embodiment, the LiBF₄ is present at a molar concentrationof from 0.5M to 3M, preferably 1.0M to 2.0M, and most preferably about1.5M. Electrolyte compositions comprising salts among those usefulherein are described in U.S. Pat. No. 5,418,091, Gozdz et al., issuedMay 23, 1995; U.S. Pat. No. 5,508,130, Golovin, issued Apr. 16, 1996;U.S. Pat. No. 5,541,020, Golovin et al., issued Jul. 30, 1996; U.S. Pat.No. 5,620,810, Golovin et al., issued Apr. 15, 1997; U.S. Pat. No.5,643,695, Barker et al., issued Jul. 1, 1997; U.S. Pat. No. 5,712,059,Barker et al., issued Jan. 27, 1997; U.S. Pat. No. 5,851,504, Barker etal., issued Dec. 22, 1998; U.S. Pat. No. 6,020,087, Gao, issued Feb. 1,2001; U.S. Pat. No. 6,103,419, Saidi et al., issued Aug. 15, 2000; andPCT Application WO 01/24305, Barker et al., published Apr. 5, 2001; allof which are incorporated by reference herein.

[0197] The electrolyte solvent contains a blend of an alkylene carbonateand a cyclic ester. The alkylene carbonates (preferably, cycliccarbonates) have a preferred ring size of from 5 to 8. The carbon atomsof the ring may be optionally substituted with C₁-C₆ carbon chains.Examples of unsubstituted cyclic carbonates are ethylene carbonate(5-membered ring), 1,3−propylene carbonate (6-membered ring),1,4-butylene carbonate (7-membered ring), and 1,5-pentylene carbonate(8-membered ring). Optionally the rings may be substituted with loweralkyl groups, preferably methyl, ethyl, propyl, or isopropyl groups.Such structures are well known; examples include a methyl substituted5-membered ring (also known as 1,2-propylene carbonate, or simplypropylene carbonate (PC)), and a dimethyl substituted 5-membered ringcarbonate (also known as 2,3-butylene carbonate) and an ethylsubstituted 5-membered ring (also known as 1,2-butylene carbonate orsimply butylene carbonate (BC). Other examples include a wide range ofmethylated, ethylated, and propylated 5-8 membered ring carbonates. In apreferred embodiment, the first component is a 5- or 6-membered ringcarbonate. More preferably, the cyclic carbonate has a 5-membered ring.In a particular preferred embodiment, the alkylene carbonate comprisesethylene carbonate.

[0198] The electrolyte solvent also comprises a cyclic ester, preferablya lactone. Preferred cyclic esters include those with ring sizes of 4 to7. The carbon atoms in the ring may be optionally substituted with C₁-C₃chains. Examples of unsubstituted cyclic esters include the 4-memberedβ-propiolactone (or simply propiolactone); γ-butrolactone (5-memberedring), δ-valerolactone (6-membered ring) and ε-caprolactone (7-memberedring). Any of the positions of the cyclic esters may be optionallysubstituted, preferably by methyl, ethyl, propyl, or isopropyl groups.Thus, preferred second components include one or more solvents selectedfrom the group of unsubstituted, methylated, ethylated, or propylatedlactones selected from the group consisting of propiolacone,butyrolactone, valerolactone, and caprolactone. (It will be appreciatedthat some of the alkylated derivatives of one lactone may be named as adifferent alkylated derivative of a different core lactone. Toillustrate, γ-butyrolactone methylated on the γ-carbon may be named asγ-valerolactone.)

[0199] In a preferred embodiment, the cyclic ester of the secondcomponent has a 5- or a 6-membered ring. Thus, preferred secondcomponent solvents include one or more compounds selected fromγ-butyrolactone (gamma-butyrolactone), and δ-valerolactone, as well asmethylated, ethylated, and propylated derivatives. Preferably, thecyclic ester has a 5-membered ring. In a particular preferredembodiment, the second component cyclic ester comprises γ-butyrolactone.

[0200] The preferred two component solvent system contains the twocomponents in a weight ratio of from about 1:20 to a ratio of about20:1. More preferably, the ratios range from about 1:10 to about 10:1and more preferably from about 1:5 to about 5:1. In a preferredembodiment the cyclic ester is present in a higher amount than thecyclic carbonate. Preferably, at least about 60% (by weight) of the twocomponent system is made up of the cyclic ester, and preferably about70% or more. In a particularly preferred embodiment, the ratio of cyclicester to cyclic carbonate is about 3 to 1. In one embodiment, thesolvent system is made up essentially of γ-butyrolactone and ethylenecarbonate. A preferred solvent system thus contains about 3 parts byweight γ-butyrolactone and about 1 part by weight ethylene carbonate.The preferred salt and solvent are used together in a preferred mixturecomprising about 1.5 molar LiBF₄ in a solvent comprising about 3 partsγ-butyrolactone and about 1 part ethylene carbonate by weight.

[0201] The solvent optionally comprises additional solvents. Suchsolvents include low molecular weight organic solvents. The optionalsolvent is preferably a compatible, relatively non-volatile, aprotic,polar solvent. Examples of such optional solvents among those usefulherein include chain carbonates such as dimethyl carbonate (DMC),diethyl carbonate (DEC), dipropylcarbonate (DPC), and ethyl methylcarbonate (EMC); ethers such as diglyme, triglyme, and tetraglyme;dimethylsulfoxide, dioxolane, sulfolane, and mixtures thereof.

[0202] A separator allows the migration of ions while still providing aphysical separation of the electric charge between the electrodes, toprevent short-circuiting. The polymeric matrix itself may function as aseparator, providing the physical isolation needed between the anode andcathode. Alternatively, the electrolyte can contain a second oradditional polymeric material to further function as a separator. In apreferred embodiment, the separator prevents damage from elevatedtemperatures within the battery that can occur due to uncontrolledreactions preferably by degrading upon high temperatures to provideinfinite resistance to prevent further uncontrolled reactions.

[0203] A separator membrane element is generally polymeric and preparedfrom a composition comprising a copolymer. A preferred compositioncontains a copolymer of about 75% to about 92% vinylidene fluoride withabout 8% to about 25% hexafluoropropylene copolymer (availablecommercially from Atochem North America as Kynar FLEX) and an organicsolvent plasticizer. Such a copolymer composition is also preferred forthe preparation of the electrode membrane elements, since subsequentlaminate interface compatibility is ensured. The plasticizing solventmay be one of the various organic compounds commonly used as solventsfor electrolyte salts, e.g., propylene carbonate or ethylene carbonate,as well as mixtures of these compounds. Higher-boiling plasticizercompounds such as dibutyl phthalate, dimethyl phthalate, diethylphthalate, and tris butoxyethyl phosphate are preferred. Inorganicfiller adjuncts, such as fumed alumina or silanized fumed silica, may beused to enhance the physical strength and melt viscosity of a separatormembrane and, in some compositions, to increase the subsequent level ofelectrolyte solution absorption. In a non-limiting example, a preferredelectrolyte separator contains about two parts polymer per one part offumed silica.

[0204] A preferred battery comprises a laminated cell structure,comprising an anode layer, a cathode layer, and electrolyte/separatorbetween the anode and cathode layers. The anode and cathode layerscomprise a current collector. A preferred current collector is a coppercollector foil, preferably in the form of an open mesh grid. The currentcollector is connected to an external current collector tab. Suchstructures are disclosed in, for example, U.S. Pat. No. 4,925,752,Fauteux et al, issued May 15, 1990; U.S. Pat. No. 5,011,501, Shackle etal., issued Apr. 30, 1991; and U.S. Pat. No. 5,326,653, Chang, issuedJul. 5, 1994; all of which are incorporated by reference herein. In abattery embodiment comprising multiple electrochemical cells, the anodetabs are preferably welded together and connected to a nickel lead. Thecathode tabs are similarly welded and connected to a welded lead,whereby each lead forms the polarized access points for the externalload.

[0205] A preferred battery comprises a laminated cell structure,comprising an anode layer, a cathode layer, and electrolyte/separatorbetween the anode and cathode layers. The anode and cathode layerscomprise a current collector. A preferred current collector is a coppercollector foil, preferably in the form of an open mesh grid. The currentcollector is connected to an external current collector tab, for adescription of tabs and collectors. Such structures are disclosed in,for example, U.S. Pat. No. 4,925,752, Fauteux et al, issued May 15,1990; U.S. Pat. No. 5,011,501, Shackle et al., issued Apr. 30, 1991; andU.S. Pat. No. 5,326,653, Chang, issued Jul. 5, 1994; all of which areincorporated by reference herein. In a battery embodiment comprisingmultiple electrochemical cells, the anode tabs are preferably weldedtogether and connected to a nickel lead. The cathode tabs are similarlywelded and connected to a welded lead, whereby each lead forms thepolarized access points for the external load.

[0206] Lamination of assembled cell structures is accomplished byconventional means by pressing between metal plates at a temperature ofabout 120-160° C. Subsequent to lamination, the battery cell materialmay be stored either with the retained plasticizer or as a dry sheetafter extraction of the plasticizer with a selective low-boiling pointsolvent. The plasticizer extraction solvent is not critical, andmethanol or ether are often used.

[0207] In a preferred embodiment, a electrode membrane comprising theelectrode active material (e.g., an insertion material such as carbon orgraphite or a insertion compound) dispersed in a polymeric bindermatrix. The electrolyte/separator film membrane is preferably aplasticized copolymer, comprising a polymeric separator and a suitableelectrolyte for ion transport. The electrolyte/separator is positionedupon the electrode element and is covered with a positive electrodemembrane comprising a composition of a finely divided lithium insertioncompound in a polymeric binder matrix. An aluminum collector foil orgrid completes the assembly. A protective bagging material covers thecell and prevents infiltration of air and moisture.

[0208] In another embodiment, a multi-cell battery configuration may beprepared with copper current collector, a negative electrode, anelectrolyte/separator, a positive electrode, and an aluminum currentcollector. Tabs of the current collector elements form respectiveterminals for the battery structure.

[0209] In a preferred embodiment of a lithium-ion battery, a currentcollector layer of aluminum foil or grid is overlaid with a positiveelectrode film, or membrane, separately prepared as a coated layer of adispersion of insertion electrode composition. This is preferably aninsertion compound such as the active material of the present inventionin powder form in a copolymer matrix solution, which is dried to formthe positive electrode. An electrolyte/separator membrane is formed as adried coating of a composition comprising a solution containing VdF:HFPcopolymer and a plasticizer solvent is then overlaid on the positiveelectrode film. A negative electrode membrane formed as a dried coatingof a powdered carbon or other negative electrode material dispersion ina VdF:HFP copolymer matrix solution is similarly overlaid on theseparator membrane layer. A copper current collector foil or grid islaid upon the negative electrode layer to complete the cell assembly.Therefore, the VdF:HFP copolymer composition is used as a binder in allof the major cell components, positive electrode film, negativeelectrode film, and electrolyte/separator membrane. The assembledcomponents are then heated under pressure to achieve heat-fusion bondingbetween the plasticized copolymer matrix electrode and electrolytecomponents, and to the collector grids, to thereby form an effectivelaminate of cell elements. This produces an essentially unitary andflexible battery cell structure.

[0210] Cells comprising electrodes, electrolytes and other materialsamong those useful herein are described in the following documents, allof which are incorporated by reference herein: U.S. Pat. No. 4,668,595,Yoshino et al., issued May 26, 1987; U.S. Pat. No. 4,792,504, Schwab etal., issued Dec. 20, 1988; U.S. Pat. No. 4,830,939, Lee et al., issuedMay 16, 1989; U.S. Pat. No. 4,935,317, Fauteaux et al., issued Jun. 19,1980; U.S. Pat. No. 4,990,413, Lee et al., issued Feb. 5, 1991; U.S.Pat. No. 5,037,712, Shackle et al., issued Aug. 6, 1991; U.S. Pat. No.5,262,253, Golovin, issued Nov. 16, 1993; U.S. Pat. No. 5,300,373,Shackle, issued Apr. 5, 1994; U.S. Pat. No. 5,399,447, Chaloner-Gill, etal., issued Mar. 21, 1995; U.S. Pat. No. 5,411,820, Chaloner-Gill,issued May 2, 1995; U.S. Pat. No. 5,435,054, Tonder et al., issued Jul.25, 1995; U.S. Pat. No. 5,463,179, Chaloner-Gill et al., issued Oct. 31,1995; U.S. Pat. No. 5,482,795, Chaloner-Gill., issued Jan. 9, 1996; U.S.Pat. No. 5,660,948, Barker, issued Sep. 16, 1995; and U.S. Pat. No.6,306,215, Larkin, issued Oct. 23, 2001. A preferred electrolyte matrixcomprises organic polymers, including VdF:HFP. Examples of casting,lamination and formation of cells using VdF:HFP are as described in U.S.Pat. Nos. 5,418,091, Gozdz et al., issued May 23, 1995; U.S. Pat. No.5,460,904, Gozdz et al., issued Oct. 24, 1995; U.S. Pat. No. 5,456,000,Gozdz et al., issued Oct. 10, 1995; and U.S. Pat. No. 5,540,741, Gozdzet al., issued Jul. 30, 1996; all of which are incorporated by referenceherein.

[0211] The electrochemical cell architecture is typically governed bythe electrolyte phase. A liquid electrolyte battery generally has acylindrical shape, with a thick protective cover to prevent leakage ofthe internal liquid. Liquid electrolyte batteries tend to be bulkierrelative to solid electrolyte batteries due to the liquid phase andextensive sealed cover. A solid electrolyte battery, is capable ofminiaturization, and can be shaped into a thin film. This capabilityallows for a much greater flexibility when shaping the battery andconfiguring the receiving apparatus. The solid state polymer electrolytecells can form flat sheets or prismatic (rectangular) packages, whichcan be modified to fit into the existing void spaces remaining inelectronic devices during the design phase.

[0212] The invention has been described above with respect to severalpreferred embodiments. Further non-limiting examples of the inventionare given in the following examples.

EXAMPLES

[0213] The general methods for preparation of the various alkalitransition metal phosphates and fluorophosphates will be described inthis section. A Siemens D500 X-ray Diffractometer equipped with Cu K_(α)radiation (λ=1.54056 A) was used for X-ray diffraction (XRD) studies ofthe prepared materials.

Example 1 Solid State Synthesis of NaVPO₄F using VPO₄

[0214] This synthesis is generally carried out in two stages—first stepto produce VPO₄ (for example by carbothermal reduction or by hydrogenreduction) followed by second step reaction with NaF. As an alternativeto using NaF, a reaction between VPO₄ and NH₄F and Na₂CO₃ was alsoinvestigated.

Example 1(a) First step: Preparation of VPO₄ by Carbothermal Reduction

[0215] The reaction is described in copending application Ser. No.09/724,085, the disclosure of which is hereby incorporated by reference.In summary the overall reaction is:

0.5V₂O₅+NH₄H₂PO₄+C→VPO₄+NH₃+1.5H₂O+CO  (1)

[0216] 31.15 g of V₂O₅, 39.35 g of NH₄H₂PO₄ (Alfa Aesar) and 4.50 g ofShawinigan black carbon (Chevron Chemical) were used. This represents a10% excess of carbon. The V₂O₅ starting material may be prepared fromthermal decomposition of ammonium metavanadate. See the discussion belowat Example 3.

[0217] The precursors were initially pre-mixed using a mortar and pestleand then pelletized. The pellet was then transferred to atemperature-controlled box oven equipped with a flowing air atmosphere.The sample was heated at a ramp rate of 2°/minute to an ultimatetemperature of 300° C. and maintained at this temperature for 3 hours.The sample was then cooled to room temperature, before being removedfrom the tube furnace. The material was recovered, re-mixed andpelletized. The pellet was then transferred to a temperature-controlledtube furnace with a flowing argon gas flow. The sample was heated at aramp rate of 2°/minute to an ultimate temperature of 750° C. andmaintained at this temperature for 8 hours. The sample was then cooledto room temperature, before being removed from the tube furnace foranalysis. The powderized sample showed good uniformity and appearedblack in color.

Example 1(b) Preparation of VPO₄ Using Hydrogen Reduction

[0218] In summary the reaction is:

0.5V₂O₅+NH₄H₂PO₄+H₂→VPO₄+NH₃+2.5H₂O  (2)

[0219] 24.92 g of V₂O₅ (Alfa Aesar) and 31.52 g of NH₄H₂PO₄ (Alfa Aesar)were used. The precursors were initially pre-mixed using a mortar andpestle and then pelletized. The pellet was then transferred to atemperature-controlled tube furnace equipped with a flowing hydrogenatmosphere. The sample was heated at a ramp rate of 2°/minute to anultimate temperature of 300° C. and maintained at this temperature for 8hours. The sample was then cooled to room temperature, before beingremoved from the tube furnace. The material was recovered, re-mixed andpelletized. The pellet was then transferred to a temperature-controlledtube furnace, again with a flowing hydrogen gas flow. The sample washeated at a ramp rate of 2°/minute to an ultimate temperature of 850° C.and maintained at this temperature for 8 hours. The sample was thencooled to room temperature, before being removed from the tube furnacefor analysis. The powderized sample showed reasonable uniformity andappeared grey in color.

Example 1(c) Preparation of NaVPO₄F by Reaction of VPO₄ and NaF

[0220] The reaction of NaF with VPO₄ to form NaVPO₄F may be performed inan inert atmosphere (e.g. argon) or in a covered crucible in a (limitedsupply) air atmosphere. Examples of each will be given below. In eithercase the overall reaction may be summarized:

NaF+VPO₄→NaVPO₄F  (3)

Example 1(c) Reaction 3.2(a): Reaction of NaF with VPO₄ to form NaVPO₄Fin an Argon Atmosphere

[0221] 5.836 g of VPO4 (Example 1(a), made by carbothermal reduction)and 1.679 g of NaF (Alfa Aesar) were used. The precursors were initiallypre-mixed using a mortar and pestle and then pelletized. The pellet wasthen transferred to a temperature-controlled tube furnace equipped witha flowing argon atmosphere. The sample was heated at a ramp rate of2o/minute to an ultimate temperature of 750° C. and maintained at thistemperature for 1 hour. The sample was then cooled to room temperature,before being removed from the tube furnace for analysis. The powderizedsample showed reasonable uniformity and appeared black in color. Inaccordance with the incorporation reaction (3), there was only a smallweight loss during reaction.

[0222]FIG. 1 shows the x-ray diffraction pattern for this material.

Example 1(d) Reaction of NaF with VPO₄ to form NaVPO₄F in a Limited AirAtmosphere

[0223]FIG. 7 shows the Synthesis Tracking Log for Sample 1S1569B1. 2.918g of VPO₄ (Example 1 (b), made by a carbothermal reduction) and 0.840 gof NaF (Alfa Aesar) were used. The precursors were initially pre-mixedusing a mortar and pestle and then pelletized. The pellet was placedinside a covered Ni crucible and then transferred to atemperature-controlled box oven in an air atmosphere. The sample washeated to an ultimate temperature of 700° C. and maintained at thistemperature for 15 minutes. The sample was then cooled to roomtemperature, before being removed from the box oven for analysis. Thepowderized sample showed good uniformity and appeared black in color. Inaccordance with the incorporation reaction (3), there was only a smallweight loss during reaction.

[0224]FIG. 2 shows the x-ray diffraction pattern for this material.

Example 2 Reaction of NaF with VPO₄ to form Na_(x)VPO₄F_(x) in a LimitedAir Atmosphere

[0225] Examples of Na_(x)VPO₄F_(x) were synthesized using 10%, 20% and50% mass excess of NaF over reaction (3).

Example 2(a) 10% excess NaF, x=1.1

[0226] 2.918 g of VPO₄ (Example 1(b), made by a carbothermal reduction)and 0.924 g of NaF (Alfa Aesar) were used. This represents anapproximate 10% mass excess over reaction (3). Thus, the productstoichiometry amounts to Na₁₁VPO₄F₁₁. The precursors were initiallypre-mixed using a mortar and pestle and then pelletized. The pellet wasplaced inside a covered Ni crucible and then transferred to atemperature-controlled box oven in an air atmosphere. The sample washeated to an ultimate temperature of 700° C. and maintained at thistemperature for 15 minutes. The sample was then cooled to roomtemperature, before being removed from the box oven for analysis. Thepowderized sample showed reasonable uniformity and appearedpredominantly black in color. In accordance with the reaction (3), therewas only a small weight loss during reaction, indicating almost fullincorporation of the NaF.

[0227]FIG. 3 shows the x-ray diffraction pattern for this material.

Example 2(b) 20% Excess NaF, x=1.2

[0228] 2.918 g of VPO₄ (made by a carbothermal reduction) and 1.008 g ofNaF (Alfa Aesar) were used. This represents an approximate a 20% massexcess over reaction (1). Thus, the product stoichiometry amounts to Na₁₂VPO₄F₁₂. The precursors were initially pre-mixed using a mortar andpestle and then pelletized. The pellet was placed inside a covered Nicrucible and then transferred to a temperature-controlled box oven in anair atmosphere. The sample was heated to an ultimate temperature of 700°C. and maintained at this temperature for 15 minutes. The sample wasthen cooled to room temperature, before being removed from the box ovenfor analysis. The powderized sample showed reasonable uniformity andappeared predominantly black in color. In accordance with the reaction(3), there was only a small weight loss during reaction indicatingalmost full incorporation of the NaF.

[0229]FIG. 4 shows an extended range x-ray diffraction pattern(2θ=10-80°) for this material.

Example 2(c) 50% Excess NaF, x=0.5

[0230] 1.460 g of VPO₄ (made by a carbothermal reduction) and 0.630 g ofNaF (Alfa Aesar) were used. This represents an approximate 50% massexcess over reaction (3). Thus, the product stoichiometry amounts toNa₁₅VPO₄F₁₅. This material is stoichiometrically equivalent to theNa₃V₂(PO₄)₂F₃ material described later. The precursors were initiallypre-mixed using a mortar and pestle and then pelletized. The pellet wasplaced inside a covered Ni crucible and then transferred to atemperature-controlled box oven in an air atmosphere. The sample washeated to an ultimate temperature of 700° C. and maintained at thistemperature for 15 minutes. The sample was then cooled to roomtemperature, before being removed from the box oven for analysis. Thepowderized sample showed reasonable uniformity and appeared green/blackin color.

Example 3 Reaction of NH₄F and Na₂CO₃ with VPO₄ to form NaVPO₄F in aLimited Air Atmosphere

[0231] The reaction of NH₄F and Na₂CO₃ with VPO₄ to form NaVPO₄F may beperformed in an inert atmosphere (e.g. argon) or in a covered cruciblein a (limited supply) air atmosphere. Examples of the latter will begiven below. The overall reaction may be summarized:

0.5Na₂CO₃+NH₄F+VPO₄→NaVPO₄F+NH₃+0.5CO₂+0.5H₂O  (4)

[0232] 1.460 g of VPO₄ (made by a carbothermal reduction), 0.370 g ofNH₄F (Alfa Aesar) and 0.530 g of Na₂CO₃ (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside a covered Ni crucible and thentransferred to a temperature-controlled box oven in an air atmosphere.The sample was heated to an ultimate temperature of 750° C. andmaintained at this temperature for 15 minutes. The sample was thencooled to room temperature, before being removed from the box oven foranalysis. The powderized sample showed good uniformity and appearedpredominantly black in color.

[0233]FIG. 5 shows the x-ray diffraction pattern for this material.

Example 4 Preparation of NaVOPO₄

[0234] The preparation of NaVOPO₄ was carried out in three stages:

Example 4(a) Thermal Decomposition of Ammonium Metavanadate, NH₄VO₃, toProduce V₂O₅

[0235] Commercial V₂O₅ exposed to atmospheric reducing agents maycontain some V⁴⁺. Although a commercial source of V₂O₅ can be used whererequired in the synthesis of the active materials of the invention, itis convenient as well to use a V₂O₅ material prepared by thermaldecomposition of ammonium metavanadate. The decomposition methodprovides a fast route to a a high-quality V₂O₅ material. The reactionfor the thermal decomposition of ammonium metavanadate is:

2.0NH₄VO₃→V₂O₅+2.0NH₃+H₂O  (5)

[0236] The ammonium metavanadate is decomposed at 500° C. in anair-filled box oven. The ammonium metavanadate is commercially availablefrom several sources such as Alfa-Aesar.

Example 4(b) Chemical Precipitation (Reflux Preparation) of α-VOPO₄.xH₂O

[0237] 40.1 g of phosphoric acid (H₃PO₄-Aldrich Chemical) is dissolvedin 200.0 g of deionized water. 7.2 g of solid V₂O₅ (from Example 4(a))is added to the phosphoric acid solution and the suspension is broughtto about 80° C. with constant stirring using a stirrer hot plate.

0.5V₂O₅+H₃PO₄+x H₂O→VOPO₄.xH₂O+1.5H₂O  (6)

[0238] After a reflux period of 16 hours the suspension was filtered andthe yellow product washed several times with cold de-ionized water.Finally the product was dried at 60° C. under a dynamic vacuum.

[0239] The drying procedure is expected to remove surface adsorbedwater, to leave the dihydrate product, VOPO₄.2H₂O. The x-ray diffractionpattern for the product is consistent with the layered tetragonalstructure expected for this material. This structure consists of sheetsof (VOPO₄)_(∞) in which each VO group is linked to four PO₄ tetrahedra.

[0240] To confirm the extent of hydration in the product material thesample was studied by thermogravimetric analysis (TGA). The sample washeated in an air atmosphere from 20° C. to 700° C. at a heating rate of10/min. For a VOPO₄.2H₂O dehydration mechanism, the weight changesexpected for the reaction:

VOPO₄.xH₂O→VOPO₄+2.0H₂O  (7)

[0241] equate to a 18.2% weight loss. In the approximate temperaturerange 20-200° C., TGA indicates two main processes, presumably relatedto sequential loss of the two moles of H₂O. The overall loss is around18.0%.

Example 4(c) Carbothermal Reduction of VOPO₄ Using Na₂CO₃ as SodiumSource

[0242] The general reaction scheme may be written:

VOPO₄+0.5Na₂CO₃+0.25C→NaVOPO₄+0.75CO₂  (8)

[0243] The reaction above is used when the desired reaction temperatureis less than about 670° C. and the carbothermal reduction proceedspredominantly via a CO₂ mechanism. Conversely, if the desired reactiontemperature is greater than about 670° C. the carbothermal reductionproceeds predominantly via a CO mechanism:

VOPO₄+0.5Na₂CO₃+0.5C→NaVOPO₄+0.5CO₂+0.5CO  (9)

[0244] The NaVOPO₄ may be produced by either of the above reactions or acombination of both. Based on the CO₂ reaction mechanism:

[0245] 1 g-mol of VOPO₄ is equivalent to 161.90 g

[0246] 2 0.5 g-mol of Na₂CO₃ is equivalent to 53.00 g

[0247] 3 0.25 g-mol of carbon is equivalent to 3.00 g

[0248] 4.86 g of VOPO₄ (dried at 200° C. to remove H₂O), 1.59 g ofNa₂CO₃ (Alfa Aesar) and 0.105 g of Shawinigan black carbon (Chevron).This represents an approximate 17% excess of carbon in the reaction. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed in a covered and sealed (to excludeambient air) Ni crucible and then transferred to atemperature-controlled box oven. The sample was heated at a ramp rate of2°/minute to an ultimate temperature of 600° C. and maintained at thistemperature for 30 minutes. The sample was then cooled to roomtemperature, before being removed from the box oven for analysis. Thepowderized sample showed reasonable uniformity and appeared black incolor.

Example 4(d) Synthesis of Na VO PO₄

[0249] NaVOPO₄ is prepared as in Example 4(c) except that the ultimatetemperature is 700° C. The powderized sample showed reasonableuniformity and appeared black in color.

Example 5 Synthesis of Li_(x)Na_(1−x)VPO₄F) Using VPO₄

[0250] The synthesis is generally carried out in two stages—first stepto produce VPO₄ (either by carbothermal reduction of by hydrogenreduction) followed by second step reaction with a mixture of LiF andNaF i.e.

x LiF+(1−x)NaF+VPO₄→Li_(x)Na_(1−x)VPO₄F  (10)

[0251] As an alternative to using alkali fluorides, a reaction betweenVPO₄ and NH₄F and a mixture of Li₂CO₃ and Na₂CO₃ may also be used. Thesynthesis of VPO₄ is described above.

Example 5(a) Li₀ ₀₅Na_(0.95)VPO₄F

[0252] Reaction of a mixture of LiF and NaF with VPO₄ to formLi_(x)Na_(1−x)VPO₄F materials in a limited air atmosphere

[0253] 1.459 g of VPO₄ (made by a carbothermal reduction), 0.013 g ofLiF (Strem Chemical) and 0.399 g of NaF (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside a covered Ni crucible and thentransferred to a temperature-controlled box oven in an air atmosphere.The sample was heated to an ultimate temperature of 700° C. andmaintained at this temperature for 15 minutes. The sample was thencooled to room temperature, before being removed from the box oven foranalysis. The powderized sample showed reasonable uniformity andappeared gray/black in color. In accordance with the incorporationreaction, there was a negligible weight loss during reaction.

[0254]FIG. 6 shows the x-ray diffraction pattern for this material.

Example 5(b) Li₀ ₀₅Na₀ ₉₅VPO₄F

[0255] 1.459 g of VPO₄ (made by a carbothermal reduction), 0.026 g ofLiF (Strem Chemical) and 0.378 g of NaF (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside a covered Ni crucible and thentransferred to a temperature-controlled box oven in an air atmosphere.The sample was heated to an ultimate temperature of 700° C. andmaintained at this temperature for 15 minutes. The sample was thencooled to room temperature, before being removed from the box oven foranalysis. The powderized sample showed reasonable uniformity andappeared black in color. In accordance with the incorporation reaction,there was a negligible weight loss during reaction.

Example 5(c) Li_(0.95)Na_(0.05)VPO₄F

[0256] 1.459 g of VPO₄ (made by a carbothermal reduction), 0.246 g ofLiF (Strem Chemical) and 0.021 g of NaF (Alfa Aesar) were used. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside a covered Ni crucible and thentransferred to a temperature-controlled box oven in an air atmosphere.The sample was heated to an ultimate temperature of 700° C. andmaintained at this temperature for 15 minutes. The sample was thencooled to room temperature, before being removed from the box oven foranalysis. The powderized sample showed reasonable uniformity andappeared black in color. In accordance with the incorporation reaction,there was a negligible weight loss during reaction.

[0257]FIG. 7 shows the x-ray diffraction pattern for this material.

Example 6 Solid State Synthesis of Na₃V₂(PO₄)₂F₃ Using VPO₄

[0258] The synthesis methods to produce Na₃V₂(PO₄)F₃ are analogous tothose used for NaVPO₄F described above, apart from the relativeproportions of reactants. It is generally carried out in two stages—afirst step to produce VPO₄ (either by carbothermal reduction of byhydrogen reduction) followed by a second step reaction with NaF. As analternative to using NaF, a reaction between VPO₄ and NH₄F and Na₂CO₃may also be used.

Example 6(a) Reaction of NaF with VPO₄ to form Na₃V₂(PO₄)₂F₃ in aLimited Air Atmosphere

[0259] 2.920 g of VPO₄ (made by a carbothermal reduction) and 1.260 g ofNaF (Alfa Aesar) were used. The precursors were initially pre-mixedusing a mortar and pestle and then pelletized. The pellet was placedinside a covered Ni crucible and then transferred to atemperature-controlled box oven in an air atmosphere. The sample washeated to an ultimate temperature of 700° C. and maintained at thistemperature for 15 minutes. The sample was then cooled to roomtemperature, before being removed from the box oven for analysis. Thepowderized sample showed reasonable uniformity and appeared gray/blackin color. In accordance with the incorporation reaction (3), there was anegligible weight loss during reaction.

[0260]FIG. 8 shows the x-ray diffraction pattern for this material.

Example 6(b) Reaction as per 6(a)

[0261] the synthesis of Example 6(a) was repeated, except thetemperature of 700° C. was maintained for one hour. The powderizedsample showed reasonable uniformity and appeared gray/black in color. Inaccordance with the incorporation reaction (3), there was a negligibleweight loss during reaction.

[0262]FIG. 9 shows the x-ray diffraction pattern for this material.

Example 7 Solid State Carbothermal Synthesis of NaFePO₄ UsingNa₂CO₃/Fe₂O₃

[0263] This expected reaction scheme may be summarized:

0.5Na₂CO₃+0.5 Fe₂O₃+(NH₄)₂HPO₄+0.5 C→NaFePO₄+2.0NH₃+0.5CO₂+CO  (11)

[0264] 1.060 g of Na₂CO₃ (Alfa Aesar), 1.600 g of Fe₂O₃ (Alfa Aesar),2.640 g of (NH₄)₂HPO₄ (Alfa Aesar) and 0.24 g of Shawinigan Black carbon(Chevron Chemical) were used. The carbon amount represents anapproximate 100% weight excess over the reaction stoichiometry. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside a covered ceramic crucible andthen transferred to a temperature-controlled tube furnace equipped witha flowing argon atmosphere. The sample was heated to an ultimatetemperature of 750° C. and maintained at this temperature for 8 hours.The sample was then cooled to room temperature, before being removedfrom the tube furnace for analysis. The powderized sample showedreasonable uniformity and appeared black in color.

Example 8 Solid State Carbothermal Synthesis of NaFePO₄ usingNaPO3/Fe₂O₃

[0265] The reaction scheme may be summarized:

NaPO₃+0.5Fe₂O₃+0.5 C→NaFePO₄+CO  (12)

[0266] 2.040 g of NaPO₃ (Alfa Aesar), 1.600 g of Fe₂O₃ (Alfa Aesar) and0.24 g of Shawinigan Black carbon (Chevron Chemical) were used. Thecarbon amount represents an approximate 100% weight excess over thereaction stoichiometry. The precursors were initially pre-mixed using amortar and pestle and then pelletized. The pellet was placed inside acovered ceramic crucible and then transferred to atemperature-controlled tube furnace equipped with a flowing argonatmosphere. The sample was heated to an ultimate temperature of 750° C.and maintained at this temperature for 8 hours. The sample was thencooled to room temperature, before being removed from the tube furnacefor analysis. The powderized sample showed reasonable uniformity andappeared black in color.

Example 9 Solid State Carbothermal Synthesis of NaFe₀ ₉Mg₀ ₁PO₄ UsingNa₂CO₃/Fe₂O₃

[0267] The reaction scheme may be summarized:

0.5Na₂CO₃+0.45Fe₂O₃+(NH₄)₂HPO₄+0.1Mg(OH)₂+0.45C→NaFe_(0.9)Mg₀ ₁PO₄+2.0NH₃+0.5CO₂+0.45CO  (13)

[0268] 0.530 g of Na₂CO₃ (Alfa Aesar), 0.719 g of Fe₂O₃ (Alfa Aesar),0.058 g of Mg(OH)₂ (Alfa Aesar) and 1.321 g of (NH₄)₂HPO₄ (Alfa Aesar)and 0.108 g of Shawinigan Black carbon (Chevron Chemical) were used. Thecarbon amount represents an approximate 100% weight excess over thereaction stoichiometry. The precursors were initially pre-mixed using amortar and pestle and then pelletized. The pellet was placed inside acovered nickel crucible (to limit exposure to the air ambient) and thentransferred to a temperature-controlled box oven. The sample was heatedto an ultimate temperature of 750° C. and maintained at this temperaturefor 30 minutes. The sample was then cooled to room temperature, beforebeing removed from the box oven for analysis. The powderized sampleshowed reasonable uniformity and appeared black in color.

Example 10 Solid State Synthesis of NaCoPO₄ Using Na₂CO₃/CoCO₃

[0269] The reaction scheme may be summarized:

0.5Na₂CO₃+CoCO₃+(NH₄)₂HPO₄→NaCoPO₄+2.0 NH₃+0.5 CO₂  (14)

[0270] 2.650 g of Na₂CO₃ (Alfa Aesar), 5.940 g of CoCO₃ (Alfa Aesar) and5.750 g of (NH₄)₂HPO₄ (Alfa Aesar) were used. The precursors wereinitially pre-mixed using a mortar and pestle and then pelletized. Thepellet was placed inside an open ceramic crucible and then transferredto a temperature-controlled tube furnace equipped with a flowing airatmosphere. The sample was heated to an ultimate temperature of 600° C.and maintained at this temperature for 8 hours. The sample was thencooled to room temperature, before being removed from the tube furnacefor analysis. The powderized sample showed good uniformity and appearedpink/purple in color.

Example 11 Solid State Synthesis of Na₃V₂(PO₄)₃ Using Na₂CO₃/V₂O₅ and H₂Atmosphere

[0271] The reaction scheme may be summarized:

1.5Na₂CO₃+V₂O₅+3.0(NH₄)₂HPO₄+2.0H₂→Na₃V₂(PO₄)₃+6.0NH₃+6.5H₂O+1.5CO₂  (15)

[0272] 7.000 g of Na₂CO₃ (Alfa Aesar), 8.000 g of V₂O₅ (Alfa Aesar) and17.300 g of (NH₄)₂HPO₄ (Alfa Aesar) were used. The precursors wereinitially pre-mixed using a mortar and pestle and then pelletized. Thepellet was placed inside an open ceramic crucible and then transferredto a temperature-controlled tube furnace equipped with a flowing purehydrogen atmosphere. The sample was heated to an ultimate temperature of170° C. and maintained at this temperature for 8 hours. The sample wasthen cooled to room temperature, before being removed from the tubefurnace. The material was re-mixed and pelletized before being returnedto the tube furnace (again equipped with a flowing pure hydrogenatmosphere). The sample was heated to an ultimate temperature of 850° C.and maintained at this temperature for 8 hours. The sample was thencooled to room temperature, before being removed from the tube furnacefor analysis. The powderized sample showed good uniformity and appearedblack in color.

Example 12 Solid State Carbothermal Synthesis of Na₃V₂(PO₄)₃ UsingNa₂CO3/V₂O₅

[0273] The reaction scheme may be summarized:

1.5Na₂CO₃+V₂O₅+3.0(NH₄)₂HPO₄+2.0C→Na₃V₂(PO₄)₃+6.0NH₃+4.5H₂O+2CO+1.5CO₂  (16)

[0274] 1.590 g of Na₂CO₃ (Alfa Aesar), 1.819 g of V₂O₅ (Alfa Aesar),3.960 g of (NH₄)₂HPO₄ (Alfa Aesar) and 0.300 g of Shawinigan Blackcarbon (Chevron Chemical) were used. The carbon amount represents anapproximate 100% weight excess over the reaction stoichiometry. Theprecursors were initially pre-mixed using a mortar and pestle and thenpelletized. The pellet was placed inside an open ceramic crucible andthen transferred to a temperature-controlled tube furnace equipped witha flowing argon atmosphere. The sample was heated to an ultimatetemperature of 850° C. and maintained at this temperature for 8 hours.The sample was then cooled to room temperature, before being removedfrom the tube furnace for analysis. The powderized sample showed gooduniformity and appeared black in color.

Example 13 Solid State Carbothermal Synthesis of Na₂FePO₄F usingNa₂CO₃/Fe₂O₃

[0275] The reaction scheme may be summarized:

0.5Na₂CO₃+1.0NaF +0.5Fe₂O₃+1.0(NH₄)₂HPO₄+0.5C→Na₂FePO₄F+2.0NH₃+1.5H₂O+0.5CO+0.5CO₂  (17)

[0276] (m) g of Na₂CO₃ (Alfa Aesar), 0.520 g of NaF (Alfa Aesar), 1.000g of Fe₂O₃ (Alfa Aesar), 1.430 g of (NH₄)₂HPO₄ (Alfa Aesar) and 0.056 gof Shawinigan Black carbon (Chevron Chemical) were used. The carbonamount represents an approximate 100% weight excess over the reactionstoichiometry. The precursors were initially pre-mixed using a mortarand pestle and then pelletized. The pellet was placed inside an openceramic crucible and then transferred to a temperature-controlled tubefurnace equipped with a flowing argon atmosphere. The sample was heatedto an ultimate temperature of 750° C. and maintained at this temperaturefor 1 hour. The sample was then cooled to room temperature, before beingremoved from the tube furnace for analysis. The powderized sample showedreasonable uniformity and appeared red/black in color.

[0277] It has been observed that the x-ray diffraction patterns aresimilar for many of the sodium transition metal phosphates andfluorophosphates synthesized above. FIG. 4 shows an extended range x-raydiffraction pattern (2θ=10-80°) of a representative example. The patternfrom this material will be used in the analysis below.

[0278] Based on a structural refinement, two possible structures weresuggested for the representative NaVPO₄F (or Na₃V₂(PO₄)₃F₂) materials.Tables 1 and 2 show the expected 2θ peaks (2θ=10-50°) and correspondingd-spacings for the two possible structures based on tetragonal andorthorhombic structures respectively. Table 1 shows the calculatedparameters for NaVPO₄F with a tetragonal structure, space group I4/mmm.The predicted lattice parameters are a=6.387 A, c=10.734 A, Z=2.

[0279] Table 2 lists the calculated parameters for NaVPO₄F withorthorhombic structure, space group I4 mm. The predicted latticeparameters for this structure are a =10.731 A, c=6.381 A.

[0280] The NaMPO₄ compounds are generally isostructural with the mineralmaricite and with the lithium analogs LiMPO₄. For instance NaFePO₄ isdescribed as orthorhombic, space group Pnma, with refined latticeparameters a =9.001 A, b=6.874 A and c=5.052 A (from Yakubovich et al.Geol. Ser. 4: 6, 54 (1992)).

[0281] The rhombehedral Na₃M₂(PO₄)₃ compounds are generallyrhombehedral, space group R3m. For instance, Masquelier et al. in Chem.Mater. 12, 525, (2000) report Na₃Fe₂(PO₄)₃ to be rhombehedral, spacegroup R3m with refined lattice parameters a =8.7270 A and c=21.8078 A.

[0282] Electrochemical Characterization in Lithium Metal Half Cells toDemonstrate Sodium Extraction Behavior:

[0283] For electrochemical evaluation purposes the active materials wereinitially cycled against a lithium metal counter electrode in alithium-containing electrolyte. The active materials were used toformulate the positive electrode. The electrode was fabricated bysolvent casting a slurry of the active material, conductive carbon,binder and solvent. The conductive carbon used was Super P (MMM Carbon).Kynar Flex 2801 was used as the binder and electronic grade acetone wasused as the solvent. The slurry was cast onto glass and a free-standingelectrode film was formed as the solvent evaporated. The proportions areas follows on a weight basis: 80% active material; 8% Super P carbon;and 12% Kynar binder.

[0284] For the lithium metal electrochemical measurements the liquidelectrolyte was Ethylene Carbonate/DiMethyl Carbonate, EC/DMC (2:1 byweight) and 1 M LiPF₆. This was used in conjunction with a Glass Fiberfilter to form the anode-cathode separator. Routine electrochemicaltesting was carried out using a commercial Maccor battery cyclerutilizing constant current cycling between pre-set voltage limits.

[0285] First cycle constant current data of the NaVPO₄F material madefrom NaF/VPO₄ in air were collected using a lithium metal counterelectrode at a current density of 0.2 mA/cm² between 3.00 and 4.50 V andare based upon 41.1 mg of the NaVPO₄F active material in the positiveelectrode. The testing was carried out at 23° C. It is demonstrated thatsodium is extracted from the NaVPO₄F during the initial charging of thecell. A charge equivalent to a material specific capacity of 97 mAh/g isextracted from the cell. It is expected from thermodynamicconsiderations that the sodium extracted from the NaVPO₄F materialduring the initial charging process, enters the electrolyte, and wouldthen be displacement ‘plated’ onto the lithium metal anode (i.e.releasing more lithium into the electrolyte). Therefore, during thesubsequent discharging of the cell, it is assumed that lithium isre-inserted into the material. The re-insertion process corresponds to85 mAh/g, indicating the reversibility of the extraction-insertionprocesses. The generally symmetrical nature of the charge-dischargecurves further indicates the excellent reversibility of the system. Fromcloser inspection of the figure it appears that sodium is extracted fromthe NaVPO₄F in two processes centered around 3.80 V vs. Li and 4.30 Vvs. Li. There also appear to be two main insertion processes, centeredat about 4.25 V vs. Li and 3.75 V vs. Li. Subsequent charge-dischargecycles show very similar steps in the voltage profile, indicating thereversibility of the material.

[0286] First cycle constant current data of the Li_(0.10)Na₀ ₀₉VPO₄Fmaterial made from LiF/NaFNPO₄ in air were collected using a lithiummetal counter electrode at a current density of 0.2 mA/cm² between 3.00and 4.50 V and are based upon 19.5 mg of the Li₀ ₁₀Na_(0.90)VPO₄F activematerial in the positive electrode. The testing was carried out at 23°C. It is demonstrated that sodium is extracted predominantly from theLi_(0.10)Na_(0.90)VPO₄F during the initial charging of the cell—althoughsome lithium will also be extracted. A charge equivalent to a materialspecific capacity of 76 mAh/g is extracted from the cell. It is expectedfrom thermodynamic considerations that the sodium extracted from the Li₀₁₀Na_(0.90)VPO₄F material during the initial charging process, entersthe electrolyte, and would then be displacement ‘plated’ onto thelithium metal anode (i.e. releasing more lithium into the electrolyte).Therefore, during the subsequent discharging of the cell, it is assumedthat lithium is re-inserted into the material. The re-insertion processcorresponds to 70 mAh/g, indicating the reversibility of theextraction-insertion processes. The generally symmetrical nature of thecharge-discharge curves further indicates the excellent reversibility ofthe system. From closer inspection of the figure it appears that sodium(plus some lithium) is extracted from the Li₀ ₁₀Na₀ ₉₀VPO₄F in twoprocesses centered around 3.80 V vs. Li and 4.30 V vs. Li. There alsoappear to be two main insertion processes, centered at about 4.25 V vs.Li and 3.75 V vs. Li. Subsequent charge-discharge cycles show verysimilar steps in the voltage profile, indicating the reversibility ofthe material.

[0287] First cycle constant current data of the Na₃V₂(PO₄)₂F₃ materialmade from NaF/VPO₄ in air at 700° C. for 15 minutes were collected usinga lithium metal counter electrode at a current density of 0.2 mA/cm²between 3.00 and 4.50 V and are based upon 24.2 mg of the Na₃V₂(PO₄)₂F₃active material in the positive electrode. The testing was carried outat 23° C. It is demonstrated that sodium is extracted from theNa₃V₂(PO₄)₂F₃ during the initial charging of the cell. A chargeequivalent to a material specific capacity of 99 mAh/g is extracted fromthe cell. It is expected from thermodynamic considerations that thesodium extracted from the Na₃V₂(PO₄)₂F₃ material during the initialcharging process, enters the electrolyte, and would then be displacement‘plated’ onto the lithium metal anode (i.e. releasing more lithium intothe electrolyte). Therefore, during the subsequent discharging of thecell, it is assumed that lithium is re-inserted into the material. There-insertion process corresponds to 86 mAh/g, indicating thereversibility of the extraction-insertion processes. The generallysymmetrical nature of the charge-discharge curves further indicates theexcellent reversibility of the system. From closer inspection of thefigure it appears that sodium is extracted from the Na₃V₂(PO₄)₂F₃ in twoprocesses centered around 3.80 V vs. Li and 4.30 V vs. Li. There alsoappear to be two main insertion processes, centered at about 4.25 V vs.Li and 3.75 V vs. Li. Subsequent charge-discharge cycles show verysimilar steps in the voltage profile, indicating the reversibility ofthe material.

[0288] First cycle constant current data of the NaVOPO₄ material madecarbothermally at 600° C. for 30 minutes were collected using a lithiummetal counter electrode at an approximate C/10 rate between 3.00 and4.60 V and are based upon 24.3 mg of the NaVOPO₄ active material in thepositive electrode. The testing was carried out at 23° C. The initialmeasured open circuit voltage (OCV) was approximately 3.20 V vs. Li. Itis demonstrated that sodium is extracted from the NaVOPO₄ during thefirst charging of the cell. A charge equivalent to a material specificcapacity of 51 mAh/g is extracted from the cell. It is expected fromthermodynamic considerations that the sodium extracted from the NaVOPO₄material during the initial charging process would be displacement‘plated’ onto the lithium metal anode. Therefore, during the subsequentdischarging of the cell, it is assumed that lithium is re-inserted intothe material. The re-insertion process corresponds to 30 mAh/g,indicating the reversibility of the extraction-insertion processes. Thegenerally symmetrical nature of the charge-discharge curves furtherindicates the reversibility of the system.

[0289] As was noted during the previous (preparative) section, NaVOPO₄may be prepared under a variety of carbothermal conditions. As acomparison the first cycle constant current data of the NaVOPO₄ materialmade carbothermally at 700° C. for 30 minutes were collected using alithium metal counter electrode at an approximate C/10 rate between 3.00and 4.60 V and are based upon 24.3 mg of the NaVOPO₄ active material inthe positive electrode. The testing was carried out at 23° C. Theinitial measured open circuit voltage (OCV) was approximately 3.25 V vs.Li. It is demonstrated that sodium is extracted from the NaVOPO₄ duringthe first charging of the cell. A charge equivalent to a materialspecific capacity of 97 mAh/g is extracted from the cell. It is expectedfrom thermodynamic considerations that the sodium extracted from theNaVOPO₄ material during the initial charging process would bedisplacement ‘plated’ onto the lithium metal anode. Therefore, duringthe subsequent discharging of the cell, it is assumed that lithium isre-inserted into the material. The re-insertion process corresponds to80 mAh/g, indicating the excellent reversibility of theextraction-insertion processes for this material. The generallysymmetrical nature of the charge-discharge curves further indicates theexcellent reversibility of the system. The improved test results forthis material over the equivalent material made at 600° C. indicates theimportance of the carbothermal preparative conditions.

[0290] First cycle constant current data of the Na₃V₂(PO₄)₃ materialmade from carbothermal reduction using Na₂CO₃ and V₂O₅ were collectedusing a lithium metal counter electrode at a current density of 0.2mA/cm² between 2.80 and 4.00 V and are based upon 27.4 mg of theNa₃V₂(PO₄)₃ active material in the positive electrode. The testing wascarried out at 23° C. It is demonstrated that sodium is extracted fromthe Na₃V₂(PO₄)₃ during the initial charging of the cell. A chargeequivalent to a material specific capacity of 91 mAh/g is extracted fromthe cell. It is expected from thermodynamic considerations that thesodium extracted from the Na₃V₂(PO₄)₃ material during the initialcharging process enters the electrolyte, and would then be displacement‘plated’ onto the lithium metal anode (i.e. releasing more lithium intothe electrolyte). Therefore, during the subsequent discharging of thecell, it is assumed that lithium is re-inserted into the material. There-insertion process corresponds to 59 mAh/g, indicating thereversibility of the extraction-insertion processes. The generallysymmetrical nature of the charge-discharge curves further indicates theexcellent reversibility of the system. From closer inspection of thefigure it appears that sodium is extracted from the Na₃V₂(PO₄)₃ in asingle process centered around 3.70 V vs. Li. There also appear to be asingle insertion processes, centered at about 3.60 V vs. Li.

[0291] Electrochemical Characterization in Sodium Ion Cells

[0292] Sodium ion cells comprise an anode, cathode and an electrolyte.The cells were constructed using a NaVPO₄F active material cathode. Thecathode material was made by the method described in section 3.1. Theanode material was the Osaka Gas hard carbon described above. For allelectrochemical cells the liquid electrolyte was EthyleneCarbonate/DiMethyl Carbonate, EC/DMC (2:1 by weight) and 1 M NaClO₄.This was used in conjunction with a Glass Fiber filter to form theanode-cathode separator. Routine electrochemical testing was carried outusing a commercial battery cycler utilizes constant current cyclingbetween pre-set voltage limits. High-resolution electrochemical data wascollected using the electrochemical voltage spectroscopy (EVS)technique. Such technique is known in the art as described in Synth.Met. D217 (1989); Synth. Met. 32, 43 (1989); J. Power Sources, 52, 185(1994); and Electrochimica Acta 40,1603 (1995).

[0293] The carbon electrode was fabricated by solvent casting a slurryof Osaka Gas hard carbon, conductive carbon, binder and casting solvent.The conductive carbon used was Super P (MMM Carbon). Kynar Flex 2801 wasused as the binder and the electronic grade acetone was used as thesolvent. The slurry was cast onto glass and a free-standing electrodefilm was formed as the solvent evaporated. The proportions for all theexample iterations shown are as follows on a weight basis: 85% activematerial; 3% Super P carbon; and 12% Kynar binder.

[0294] A representative test cell contained 41.1 mg of active NaVPO₄Fand 15.4 mg of active hard carbon for a cathode to anode mass ratio of2.67:1. The cell was charged and discharged using constant currentconditions at 23° C. with an approximate C/10 (10 hour) rate betweenvoltage limits of 2.50 V and 4.25 V. FIG. 11 shows the variation in cellvoltage versus cathode specific capacity for the sodium ion cell undertest. The discharge process corresponds to a specific capacity for thecathode of 79 mAh/g while the charge process corresponds to a cathodespecific capacity of 82 mAh/g. This represents good reversibleperformance. The hard carbon cycles reversibly at an approximatespecific capacity of 219 mAh/g. The cell continues to cycle well afterthese initial cycles.

[0295] The NaVPO₄F/hard carbon sodium ion system was further evaluatedusing the EVS method. A representative test cell contained 44.7 mg ofactive NaVPO₄F and 18.2 mg of active hard carbon for a cathode to anodemass ratio of 2.46:1. The cell was charged and discharged using EVSconditions at 23° C. with an approximate C/10 (10 hour) rate betweenvoltage limits of 2.00 V and 4.30 V. FIG. 12 shows the variation in cellvoltage versus cathode specific capacity for the sodium ion cell undertest. The discharge process corresponds to a specific capacity for thecathode of 82 mAh/g, while the charge process corresponds to a cathodespecific capacity of 82 mAh/g. Thus for the EVS cycle shown in thefigure, the process is demonstrated to be coulombically efficient. Thisis an extremely good and reversible performance. The hard carbon cyclesreversibly at an approximate specific capacity of 202 mAh/g.

[0296]FIG. 13 shows the corresponding EVS differential capacity data forthe sodium ion cell and demonstrates the reversibility of the system.The cell charge process is shown above the O-axis (i.e. positivedifferential capacity data), while the discharge process is below theaxis (i.e. negative differential capacity data). The overallcharge-discharge process appears reversible, and no features are presentin the figure which suggest irreversible cell reactions are takingplace.

[0297] The invention has been described above with respect to certainpreferred embodiments. Based on the description, variations,modifications, and substitutions will be apparent to those of skill inthe art that are also within the scope of the invention, which isdefined by and limited only in the attached claims.

We claim:
 1. A battery comprising a positive electrode, a negativeelectrode and an electrolyte wherein: the positive electrode comprisesan electrochemically active material that can reversibly cycle sodiumions; and wherein the negative electrode comprises a carbon capable ofinserting sodium ions and that cycles reversibly at a specific capacitygreater than 100 mAh/g.
 2. A battery according to claim 1, wherein thenegative electrode cycles reversibly at a specific capacity greater than200 mAh/g.
 3. A battery according to claim 1, wherein the negativeelectrode cycles reversibly at a specific capacity greater than 300mAh/g.
 4. A battery according to claim 1, wherein the carbon of thenegative electrode is characterized by having an interlayer spacing d₀₀₂greater than that found in crystalline graphite.
 5. A battery accordingto claim 1, wherein the carbon is characterized by having an x-raydiffraction pattern having a 002 peak centered at about 24.2 degrees 2θand a 004 peak centered at about 43.3 degrees 2θ.
 6. A battery accordingto claim 1, wherein the electrochemically active material comprises asodium transition metal phosphate.
 7. A battery according to claim 6,wherein the transition metal comprises a transition metal selected fromthe group consisting of vanadium, manganese, iron, cobalt, copper,nickel, titanium, and mixtures thereof.
 8. A battery according to claim1, wherein the electrochemically active material comprises a sodiumtransition metal fluorophosphate.
 9. A battery according to claim 8,wherein the transition metal comprises a transition metal selected fromthe group consisting of cobalt, iron, vanadium, manganese, copper,nickel, titanium, and mixtures thereof.
 10. A battery according to claim1, wherein the electrochemically active material comprises a sodiumvanadium compound.
 11. A battery according to claim 1 wherein theelectrochemically active material comprises a material of formulaNa_(1+y)MPO₄ F_(1+y) wherein y is from −0.2 to 0.5 and M comprises atransition metal selected from the group consisting of V, Mn, Fe, Co,Cu, Ni, Ti, and mixtures thereof.
 12. A battery according to claim 11,wherein M comprises vanadium.
 13. A battery according to claim 1,whereinthe electrochemically active material has general formula Na₃M₂(PO₄)₃wherein M comprises a transition metal group consisting of V, Mn, Fe,Co, Cu, Ni, Ti, and mixtures thereof.
 14. A battery according to claim13, wherein M comprises vanadium.
 15. A battery according to claim 1,wherein the electrochemically active material comprises a compound offormula NaFe_(x)Mg_(1−x)PO₄ wherein 0<x<1.
 16. A battery according toclaim 1 wherein the electrochemically active material comprises amaterial of formula Li_(1−z)Na_(z)MPO₄F wherein 0<z<1, and M comprises atransition metal selected from the group consisting of V, Mn, Fe, Co,Cu, Ni, Ti, and mixtures thereof.
 17. A battery comprising a positiveelectrode, a negative electrode, and an electrolyte, wherein thepositive electrode comprises an electrochemically active material thatcan reversibly cycle sodium ions; and wherein the negative electrodecomprises a material capable of accepting and releasing sodium ions;wherein the electrochemically active material comprises at least onecompound of the formula: A_(a)M_(b)(XY₄)_(c)Z_(d), wherein (a) A isselected from the group consisting of Li, Na, K, and mixtures thereof,and 0<a≦9; (b) M comprises one or more metals, comprising at least onemetal which is capable of undergoing oxidation to a higher valencestate, and 1≦b≦3; (c) XY₄ is selected from the group consisting ofX′O_(4−x)Y′_(x), X′O_(4−y)Y′_(2y), X″S₄, and mixtures thereof, where X′is selected from the group consisting of P, As, Sb, Si, V, Ge, S, andmixtures thereof; X″ is selected from the group consisting of P, As, Sb,Si, V, Ge and mixtures thereof; Y′ is selected from the group consistingof halogen, S, N, and mixtures thereof; 0≦x<3; and 0<y≦2; and 0<c≦3; (d)Z is OH, halogen, or mixtures thereof, and 0≦d≦6; and wherein M, XY₄, Z,a, b, c, d, x and y are selected so as to maintain electroneutrality ofsaid compound.
 18. A battery according to claim 17 wherein XY₄ comprisesphosphate.
 19. A battery according to claim 17 wherein XY₄ comprises ananion selected from the group consisting of phosphate, silicate,sulfate, and mixtures thereof.
 20. A battery according to claim 17,wherein XY₄ comprises an anion selected from the group consisting ofX′O_(4−x)Y′_(x) with x greater than zero, X′O_(4−y)Y′_(2y) with ygreater than zero, X″S₄ and mixtures thereof.
 21. A battery according toclaim 17, wherein d=0.
 22. A battery according to claim 17, wherein d>0.23. A battery according to claim 17, wherein b is about 2 and c is about3.
 24. A battery according to claim 17, wherein b is about 1 and c isabout
 1. 25. A battery according to claim 17, wherein the material ofthe negative electrode reversibly cycles sodium ions at a specificcapacity greater than about 100 mAh/g.
 26. A battery according to claim17 wherein the material of the negative electrode reversibly cyclessodium ions at a specific capacity greater than about 200 mAh/g.
 27. Abattery according to claim 17 wherein the material of the negativeelectrode comprises carbon characterized by having an interlayer spacingd₀₀₂ greater than that found in crystalline graphite.
 28. A batteryaccording to claim 27, wherein the carbon is characterized as having anx-ray diffraction pattern with a 002 reflection centered at about 24.4°2θ and a 004 reflection centered at about 43.3° 2θ.
 29. A batterycomprising a positive electrode, a negative electrode, and anelectrolyte, wherein the positive electrode comprises an active materialof formula A_(a)M_(b)(XY₄)_(c)Z_(d), wherein (a) A is selected from thegroup consisting of Na and mixtures of Na and Li, and 0<a≦9; (b) Mcomprises one or more metals, comprising at least one metal capable ofundergoing oxidation to a higher valence state, and 1≦b≦3; (c) XY₄ isselected from the group consisting of X′O_(4−x)Y′_(x), X′O_(4−y)Y′_(2y),X″S₄, and mixtures thereof, where X′ is selected from the groupconsisting of P, As, Sb, Si, V, Ge, S, and mixtures thereof; X″ isselected from the group consisting of P, As, Sb, Si, V, Ge and mixturesthereof; Y′ is selected from the group consisting of halogen, S, N, andmixtures thereof; 0≦x<3; and 0<y≦2; and 0<c≦3; (d) Z is OH, halogen, ormixtures thereof, and 0≦d≦6; and wherein M, XY₄, Z, a, b, c, d, x and yare selected so as to maintain electroneutrality of said compound.
 30. Abattery according to claim 29, wherein the active material has formulaLi_(1−z)Na_(z)MPO₄ wherein z is greater than
 0. 31. A battery accordingto claim 30, wherein M comprises a metal selected from the groupconsisting of V, Mn, Fe, Co, Cu, Ni, Ti, and mixtures thereof.
 32. Abattery according to claim 29, wherein the negative electrode comprisesa carbon material capable of cycling sodium ions at a specific capacityof 100 mAh/g or greater.
 33. A battery according to claim 29, whereinthe electrolyte comprises a source of mobile lithium ions.
 34. A batteryaccording to claim 29, wherein the positive electrode material cycleslithium ions and sodium ions.
 35. A battery according to claim 29,wherein the negative electrode comprises an insertion material thatcycles lithium and sodium ions.